Adding upstream version 3.1.0.upstream/3.1.0

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

13 files changed, 1536 insertions, 0 deletions

diff --git a/.coveragerc b/.coveragerc
new file mode 100644
index 0000000..0bada6e
--- /dev/null
+++ b/.coveragerc
@@ -0,0 +1,33 @@
+[run]
+branch = True
+source =
+    .
+omit =
+    .tox/*
+    /usr/*
+    setup.py
+    # Don't complain if non-runnable code isn't run
+    */__main__.py
+
+[report]
+show_missing = True
+skip_covered = True
+exclude_lines =
+    # Have to re-enable the standard pragma
+    \#\s*pragma: no cover
+    # We optionally substitute this
+    ${COVERAGE_IGNORE_WINDOWS}
+
+    # Don't complain if tests don't hit defensive assertion code:
+    ^\s*raise AssertionError\b
+    ^\s*raise NotImplementedError\b
+    ^\s*return NotImplemented\b
+    ^\s*raise$
+
+    # Don't complain if non-runnable code isn't run:
+    ^if __name__ == ['"]__main__['"]:$
+
+[html]
+directory = coverage-html
+
+# vim:ft=dosini
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..4b9703a
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,6 @@
+*.egg-info
+*.pyc
+/.pytest_cache
+/.coverage
+/.tox
+/venv*
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
new file mode 100644
index 0000000..948de77
--- /dev/null
+++ b/.pre-commit-config.yaml
@@ -0,0 +1,38 @@
+repos:
+-   repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v2.5.0
+    hooks:
+    -   id: trailing-whitespace
+    -   id: end-of-file-fixer
+    -   id: check-docstring-first
+    -   id: check-yaml
+    -   id: debug-statements
+    -   id: name-tests-test
+    -   id: requirements-txt-fixer
+-   repo: https://gitlab.com/pycqa/flake8
+    rev: 3.7.9
+    hooks:
+    -   id: flake8
+-   repo: https://github.com/pre-commit/mirrors-autopep8
+    rev: v1.5
+    hooks:
+    -   id: autopep8
+-   repo: https://github.com/asottile/reorder_python_imports
+    rev: v1.9.0
+    hooks:
+    -   id: reorder-python-imports
+        args: [--py3-plus]
+-   repo: https://github.com/asottile/pyupgrade
+    rev: v1.26.2
+    hooks:
+    -   id: pyupgrade
+        args: [--py36-plus]
+-   repo: https://github.com/asottile/add-trailing-comma
+    rev: v1.5.0
+    hooks:
+    -   id: add-trailing-comma
+        args: [--py36-plus]
+-   repo: https://github.com/asottile/setup-cfg-fmt
+    rev: v1.6.0
+    hooks:
+    -   id: setup-cfg-fmt
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..b7af5ef
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,19 @@
+Copyright (c) 2018 Anthony Sottile
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..2b8f227
--- /dev/null
+++ b/README.md
@@ -0,0 +1,282 @@
+[![Build Status](https://dev.azure.com/asottile/asottile/_apis/build/status/asottile.cfgv?branchName=master)](https://dev.azure.com/asottile/asottile/_build/latest?definitionId=24&branchName=master)
+[![Azure DevOps coverage](https://img.shields.io/azure-devops/coverage/asottile/asottile/24/master.svg)](https://dev.azure.com/asottile/asottile/_build/latest?definitionId=24&branchName=master)
+
+cfgv
+====
+
+Validate configuration and produce human readable error messages.
+
+## Installation
+
+`pip install cfgv`
+
+## Sample error messages
+
+These are easier to see by example.  Here's an example where I typo'd `true`
+in a [pre-commit](https://pre-commit.com) configuration.
+
+```
+pre_commit.clientlib.InvalidConfigError:
+==> File /home/asottile/workspace/pre-commit/.pre-commit-config.yaml
+==> At Config()
+==> At key: repos
+==> At Repository(repo='https://github.com/pre-commit/pre-commit-hooks')
+==> At key: hooks
+==> At Hook(id='flake8')
+==> At key: always_run
+=====> Expected bool got str
+```
+
+## API
+
+### `cfgv.validate(value, schema)`
+
+Perform validation on the schema:
+- raises `ValidationError` on failure
+- returns the value on success (for convenience)
+
+### `cfgv.apply_defaults(value, schema)`
+
+Returns a new value which sets all missing optional values to their defaults.
+
+### `cfgv.remove_defaults(value, schema)`
+
+Returns a new value which removes all optional values that are set to their
+defaults.
+
+### `cfgv.load_from_filename(filename, schema, load_strategy, exc_tp=ValidationError)`
+
+Load a file given the `load_strategy`.  Reraise any errors as `exc_tp`.  All
+defaults will be populated in the resulting value.
+
+Most useful when used with `functools.partial` as follows:
+
+```python
+load_my_cfg = functools.partial(
+    cfgv.load_from_filename,
+    schema=MY_SCHEMA,
+    load_strategy=json.loads,
+    exc_tp=MyError,
+)
+```
+
+## Making a schema
+
+A schema validates a container -- `cfgv` provides `Map` and `Array` for
+most normal cases.
+
+### writing your own schema container
+
+If the built-in containers below don't quite satisfy your usecase, you can
+always write your own.  Containers use the following interface:
+
+```python
+class Container(object):
+    def check(self, v):
+        """check the passed in value (do not modify `v`)"""
+
+    def apply_defaults(self, v):
+        """return a new value with defaults applied (do not modify `v`)"""
+
+    def remove_defaults(self, v):
+        """return a new value with defaults removed (do not modify `v`)"""
+```
+
+### `Map(object_name, id_key, *items)`
+
+The most basic building block for creating a schema is a `Map`
+
+- `object_name`: will be displayed in error messages
+- `id_key`: will be used to identify the object in error messages.  Set to
+  `None` if there is no identifying key for the object.
+- `items`: validator objects such as `Required` or `Optional`
+
+Consider the following schema:
+
+```python
+Map(
+    'Repo', 'url',
+    Required('url', check_any),
+)
+```
+
+In an error message, the map may be displayed as:
+
+- `Repo(url='https://github.com/pre-commit/pre-commit')`
+- `Repo(url=MISSING)` (if the key is not present)
+
+### `Array(of, allow_empty=True)`
+
+Used to nest maps inside of arrays.  For arrays of scalars, see `check_array`.
+
+- `of`: A `Map` / `Array` or other sub-schema.
+- `allow_empty`: when `False`, `Array` will ensure at least one element.
+
+When validated, this will check that each element adheres to the sub-schema.
+
+## Validator objects
+
+Validator objects are used to validate key-value-pairs of a `Map`.
+
+### writing your own validator
+
+If the built-in validators below don't quite satisfy your usecase, you can
+always write your own.  Validators use the following interface:
+
+```python
+class Validator(object):
+    def check(self, dct):
+        """check that your specific key has the appropriate value in `dct`"""
+
+    def apply_default(self, dct):
+        """modify `dct` and set the default value if it is missing"""
+
+    def remove_default(self, dct):
+        """modify `dct` and remove the default value if it is present"""
+```
+
+It may make sense to _borrow_ functions from the built in validators.  They
+additionally use the following interface(s):
+
+- `self.key`: the key to check
+- `self.check_fn`: the [check function](#check-functions)
+- `self.default`: a default value to set.
+
+### `Required(key, check_fn)`
+
+Ensure that a key is present in a `Map` and adheres to the
+[check function](#check-functions).
+
+### `RequiredRecurse(key, schema)`
+
+Similar to `Required`, but uses a [schema](#making-a-schema).
+
+### `Optional(key, check_fn, default)`
+
+If a key is present, check that it adheres to the
+[check function](#check-functions).
+
+- `apply_defaults` will set the `default` if it is not present.
+- `remove_defaults` will remove the value if it is equal to `default`.
+
+### `OptionalRecurse(key, schema, default)`
+
+Similar to `Optional` but uses a [schema](#making-a-schema).
+
+- `apply_defaults` will set the `default` if it is not present and then
+  validate it with the schema.
+- `remove_defaults` will remove defaults using the schema, and then remove the
+  value it if it is equal to `default`.
+
+### `OptionalNoDefault(key, check_fn)`
+
+Like `Optional`, but does not `apply_defaults` or `remove_defaults`.
+
+### `Conditional(key, check_fn, condition_key, condition_value, ensure_absent=False)`
+
+- If `condition_key` is equal to the `condition_value`, the specific `key`
+will be checked using the [check function](#check-functions).
+- If `ensure_absent` is `True` and the condition check fails, the `key` will
+be checked for absense.
+
+Note that the `condition_value` is checked for equality, so any object
+implementing `__eq__` may be used.  A few are provided out of the box
+for this purpose, see [equality helpers](#equality-helpers).
+
+### `ConditionalOptional(key, check_fn, default, condition_key, condition_value, ensure_absent=False)`
+
+Similar to ``Conditional`` and ``Optional``.
+
+### `ConditionalRecurse(key, schema, condition_key, condition_value, ensure_absent=True)`
+
+Similar to `Conditional`, but uses a [schema](#making-a-schema).
+
+### `NoAdditionalKeys(keys)`
+
+Use in a mapping to ensure that only the `keys` specified are present.
+
+## Equality helpers
+
+Equality helpers at the very least implement `__eq__` for their behaviour.
+
+They may also implement `def describe_opposite(self):` for use in the
+`ensure_absent=True` error message (otherwise, the `__repr__` will be used).
+
+### `Not(val)`
+
+Returns `True` if the value is not equal to `val`.
+
+### `In(*values)`
+
+Returns `True` if the value is contained in `values`.
+
+### `NotIn(*values)`
+
+Returns `True` if the value is not contained in `values`.
+
+## Check functions
+
+A number of check functions are provided out of the box.
+
+A check function takes a single parameter, the `value`, and either raises a
+`ValidationError` or returns nothing.
+
+### `check_any(_)`
+
+A noop check function.
+
+### `check_type(tp, typename=None)`
+
+Returns a check function to check for a specific type.  Setting `typename`
+will replace the type's name in the error message.
+
+For example:
+
+```python
+Required('key', check_type(int))
+# 'Expected bytes' in both python2 and python3.
+Required('key', check_type(bytes, typename='bytes'))
+```
+
+Several type checking functions are provided out of the box:
+
+- `check_bool`
+- `check_bytes`
+- `check_int`
+- `check_string`
+- `check_text`
+
+### `check_one_of(possible)`
+
+Returns a function that checks that the value is contained in `possible`.
+
+For example:
+
+```python
+Required('language', check_one_of(('javascript', 'python', 'ruby')))
+```
+
+### `check_regex(v)`
+
+Ensures that `v` is a valid python regular expression.
+
+### `check_array(inner_check)`
+
+Returns a function that checks that a value is a sequence and that each
+value in that sequence adheres to the `inner_check`.
+
+For example:
+
+```python
+Required('args', check_array(check_string))
+```
+
+### `check_and(*fns)`
+
+Returns a function that performs multiple checks on a value.
+
+For example:
+
+```python
+Required('language', check_and(check_string, my_check_language))
+```
diff --git a/azure-pipelines.yml b/azure-pipelines.yml
new file mode 100644
index 0000000..ebca7d2
--- /dev/null
+++ b/azure-pipelines.yml
@@ -0,0 +1,20 @@
+trigger:
+  branches:
+    include: [master, test-me-*]
+  tags:
+    include: ['*']
+
+resources:
+  repositories:
+    - repository: asottile
+      type: github
+      endpoint: github
+      name: asottile/azure-pipeline-templates
+      ref: refs/tags/v1.0.1
+
+jobs:
+- template: job--pre-commit.yml@asottile
+- template: job--python-tox.yml@asottile
+  parameters:
+    toxenvs: [pypy3, py36, py37, py38]
+    os: linux
diff --git a/cfgv.py b/cfgv.py
new file mode 100644
index 0000000..64c2380
--- /dev/null
+++ b/cfgv.py
@@ -0,0 +1,408 @@
+import collections
+import contextlib
+import os.path
+import re
+import sys
+
+
+class ValidationError(ValueError):
+    def __init__(self, error_msg, ctx=None):
+        super().__init__(error_msg)
+        self.error_msg = error_msg
+        self.ctx = ctx
+
+    def __str__(self):
+        out = '\n'
+        err = self
+        while err.ctx is not None:
+            out += f'==> {err.ctx}\n'
+            err = err.error_msg
+        out += f'=====> {err.error_msg}'
+        return out
+
+
+MISSING = collections.namedtuple('Missing', ())()
+type(MISSING).__repr__ = lambda self: 'MISSING'
+
+
+@contextlib.contextmanager
+def validate_context(msg):
+    try:
+        yield
+    except ValidationError as e:
+        _, _, tb = sys.exc_info()
+        raise ValidationError(e, ctx=msg).with_traceback(tb)
+
+
+@contextlib.contextmanager
+def reraise_as(tp):
+    try:
+        yield
+    except ValidationError as e:
+        _, _, tb = sys.exc_info()
+        raise tp(e).with_traceback(tb)
+
+
+def _dct_noop(self, dct):
+    pass
+
+
+def _check_optional(self, dct):
+    if self.key not in dct:
+        return
+    with validate_context(f'At key: {self.key}'):
+        self.check_fn(dct[self.key])
+
+
+def _apply_default_optional(self, dct):
+    dct.setdefault(self.key, self.default)
+
+
+def _remove_default_optional(self, dct):
+    if dct.get(self.key, MISSING) == self.default:
+        del dct[self.key]
+
+
+def _require_key(self, dct):
+    if self.key not in dct:
+        raise ValidationError(f'Missing required key: {self.key}')
+
+
+def _check_required(self, dct):
+    _require_key(self, dct)
+    _check_optional(self, dct)
+
+
+@property
+def _check_fn_recurse(self):
+    def check_fn(val):
+        validate(val, self.schema)
+    return check_fn
+
+
+def _apply_default_required_recurse(self, dct):
+    dct[self.key] = apply_defaults(dct[self.key], self.schema)
+
+
+def _remove_default_required_recurse(self, dct):
+    dct[self.key] = remove_defaults(dct[self.key], self.schema)
+
+
+def _apply_default_optional_recurse(self, dct):
+    if self.key not in dct:
+        _apply_default_optional(self, dct)
+    _apply_default_required_recurse(self, dct)
+
+
+def _remove_default_optional_recurse(self, dct):
+    if self.key in dct:
+        _remove_default_required_recurse(self, dct)
+        _remove_default_optional(self, dct)
+
+
+def _get_check_conditional(inner):
+    def _check_conditional(self, dct):
+        if dct.get(self.condition_key, MISSING) == self.condition_value:
+            inner(self, dct)
+        elif (
+                self.condition_key in dct and
+                self.ensure_absent and self.key in dct
+        ):
+            if hasattr(self.condition_value, 'describe_opposite'):
+                explanation = self.condition_value.describe_opposite()
+            else:
+                explanation = f'is not {self.condition_value!r}'
+            raise ValidationError(
+                f'Expected {self.key} to be absent when {self.condition_key} '
+                f'{explanation}, found {self.key}: {dct[self.key]!r}',
+            )
+    return _check_conditional
+
+
+def _apply_default_conditional_optional(self, dct):
+    if dct.get(self.condition_key, MISSING) == self.condition_value:
+        _apply_default_optional(self, dct)
+
+
+def _remove_default_conditional_optional(self, dct):
+    if dct.get(self.condition_key, MISSING) == self.condition_value:
+        _remove_default_optional(self, dct)
+
+
+def _apply_default_conditional_recurse(self, dct):
+    if dct.get(self.condition_key, MISSING) == self.condition_value:
+        _apply_default_required_recurse(self, dct)
+
+
+def _remove_default_conditional_recurse(self, dct):
+    if dct.get(self.condition_key, MISSING) == self.condition_value:
+        _remove_default_required_recurse(self, dct)
+
+
+def _no_additional_keys_check(self, dct):
+    extra = sorted(set(dct) - set(self.keys))
+    if extra:
+        extra_s = ', '.join(str(x) for x in extra)
+        keys_s = ', '.join(str(x) for x in self.keys)
+        raise ValidationError(
+            f'Additional keys found: {extra_s}.  '
+            f'Only these keys are allowed: {keys_s}',
+        )
+
+
+def _warn_additional_keys_check(self, dct):
+    extra = sorted(set(dct) - set(self.keys))
+    if extra:
+        self.callback(extra, self.keys, dct)
+
+
+Required = collections.namedtuple('Required', ('key', 'check_fn'))
+Required.check = _check_required
+Required.apply_default = _dct_noop
+Required.remove_default = _dct_noop
+RequiredRecurse = collections.namedtuple('RequiredRecurse', ('key', 'schema'))
+RequiredRecurse.check = _check_required
+RequiredRecurse.check_fn = _check_fn_recurse
+RequiredRecurse.apply_default = _apply_default_required_recurse
+RequiredRecurse.remove_default = _remove_default_required_recurse
+Optional = collections.namedtuple('Optional', ('key', 'check_fn', 'default'))
+Optional.check = _check_optional
+Optional.apply_default = _apply_default_optional
+Optional.remove_default = _remove_default_optional
+OptionalRecurse = collections.namedtuple(
+    'OptionalRecurse', ('key', 'schema', 'default'),
+)
+OptionalRecurse.check = _check_optional
+OptionalRecurse.check_fn = _check_fn_recurse
+OptionalRecurse.apply_default = _apply_default_optional_recurse
+OptionalRecurse.remove_default = _remove_default_optional_recurse
+OptionalNoDefault = collections.namedtuple(
+    'OptionalNoDefault', ('key', 'check_fn'),
+)
+OptionalNoDefault.check = _check_optional
+OptionalNoDefault.apply_default = _dct_noop
+OptionalNoDefault.remove_default = _dct_noop
+Conditional = collections.namedtuple(
+    'Conditional',
+    ('key', 'check_fn', 'condition_key', 'condition_value', 'ensure_absent'),
+)
+Conditional.__new__.__defaults__ = (False,)
+Conditional.check = _get_check_conditional(_check_required)
+Conditional.apply_default = _dct_noop
+Conditional.remove_default = _dct_noop
+ConditionalOptional = collections.namedtuple(
+    'ConditionalOptional',
+    (
+        'key', 'check_fn', 'default', 'condition_key', 'condition_value',
+        'ensure_absent',
+    ),
+)
+ConditionalOptional.__new__.__defaults__ = (False,)
+ConditionalOptional.check = _get_check_conditional(_check_optional)
+ConditionalOptional.apply_default = _apply_default_conditional_optional
+ConditionalOptional.remove_default = _remove_default_conditional_optional
+ConditionalRecurse = collections.namedtuple(
+    'ConditionalRecurse',
+    ('key', 'schema', 'condition_key', 'condition_value', 'ensure_absent'),
+)
+ConditionalRecurse.__new__.__defaults__ = (False,)
+ConditionalRecurse.check = _get_check_conditional(_check_required)
+ConditionalRecurse.check_fn = _check_fn_recurse
+ConditionalRecurse.apply_default = _apply_default_conditional_recurse
+ConditionalRecurse.remove_default = _remove_default_conditional_recurse
+NoAdditionalKeys = collections.namedtuple('NoAdditionalKeys', ('keys',))
+NoAdditionalKeys.check = _no_additional_keys_check
+NoAdditionalKeys.apply_default = _dct_noop
+NoAdditionalKeys.remove_default = _dct_noop
+WarnAdditionalKeys = collections.namedtuple(
+    'WarnAdditionalKeys', ('keys', 'callback'),
+)
+WarnAdditionalKeys.check = _warn_additional_keys_check
+WarnAdditionalKeys.apply_default = _dct_noop
+WarnAdditionalKeys.remove_default = _dct_noop
+
+
+class Map(collections.namedtuple('Map', ('object_name', 'id_key', 'items'))):
+    __slots__ = ()
+
+    def __new__(cls, object_name, id_key, *items):
+        return super().__new__(cls, object_name, id_key, items)
+
+    def check(self, v):
+        if not isinstance(v, dict):
+            raise ValidationError(
+                f'Expected a {self.object_name} map but got a '
+                f'{type(v).__name__}',
+            )
+        if self.id_key is None:
+            context = f'At {self.object_name}()'
+        else:
+            key_v_s = v.get(self.id_key, MISSING)
+            context = f'At {self.object_name}({self.id_key}={key_v_s!r})'
+        with validate_context(context):
+            for item in self.items:
+                item.check(v)
+
+    def apply_defaults(self, v):
+        ret = v.copy()
+        for item in self.items:
+            item.apply_default(ret)
+        return ret
+
+    def remove_defaults(self, v):
+        ret = v.copy()
+        for item in self.items:
+            item.remove_default(ret)
+        return ret
+
+
+class Array(collections.namedtuple('Array', ('of', 'allow_empty'))):
+    __slots__ = ()
+
+    def __new__(cls, of, allow_empty=True):
+        return super().__new__(cls, of=of, allow_empty=allow_empty)
+
+    def check(self, v):
+        check_array(check_any)(v)
+        if not self.allow_empty and not v:
+            raise ValidationError(
+                f"Expected at least 1 '{self.of.object_name}'",
+            )
+        for val in v:
+            validate(val, self.of)
+
+    def apply_defaults(self, v):
+        return [apply_defaults(val, self.of) for val in v]
+
+    def remove_defaults(self, v):
+        return [remove_defaults(val, self.of) for val in v]
+
+
+class Not(collections.namedtuple('Not', ('val',))):
+    __slots__ = ()
+
+    def describe_opposite(self):
+        return f'is {self.val!r}'
+
+    def __eq__(self, other):
+        return other is not MISSING and other != self.val
+
+
+class NotIn(collections.namedtuple('NotIn', ('values',))):
+    __slots__ = ()
+
+    def __new__(cls, *values):
+        return super().__new__(cls, values=values)
+
+    def describe_opposite(self):
+        return f'is any of {self.values!r}'
+
+    def __eq__(self, other):
+        return other is not MISSING and other not in self.values
+
+
+class In(collections.namedtuple('In', ('values',))):
+    __slots__ = ()
+
+    def __new__(cls, *values):
+        return super().__new__(cls, values=values)
+
+    def describe_opposite(self):
+        return f'is not any of {self.values!r}'
+
+    def __eq__(self, other):
+        return other is not MISSING and other in self.values
+
+
+def check_any(_):
+    pass
+
+
+def check_type(tp, typename=None):
+    def check_type_fn(v):
+        if not isinstance(v, tp):
+            typename_s = typename or tp.__name__
+            raise ValidationError(
+                f'Expected {typename_s} got {type(v).__name__}',
+            )
+    return check_type_fn
+
+
+check_bool = check_type(bool)
+check_bytes = check_type(bytes)
+check_int = check_type(int)
+check_string = check_type(str, typename='string')
+check_text = check_type(str, typename='text')
+
+
+def check_one_of(possible):
+    def check_one_of_fn(v):
+        if v not in possible:
+            possible_s = ', '.join(str(x) for x in sorted(possible))
+            raise ValidationError(
+                f'Expected one of {possible_s} but got: {v!r}',
+            )
+    return check_one_of_fn
+
+
+def check_regex(v):
+    try:
+        re.compile(v)
+    except re.error:
+        raise ValidationError(f'{v!r} is not a valid python regex')
+
+
+def check_array(inner_check):
+    def check_array_fn(v):
+        if not isinstance(v, (list, tuple)):
+            raise ValidationError(
+                f'Expected array but got {type(v).__name__!r}',
+            )
+
+        for i, val in enumerate(v):
+            with validate_context(f'At index {i}'):
+                inner_check(val)
+    return check_array_fn
+
+
+def check_and(*fns):
+    def check(v):
+        for fn in fns:
+            fn(v)
+    return check
+
+
+def validate(v, schema):
+    schema.check(v)
+    return v
+
+
+def apply_defaults(v, schema):
+    return schema.apply_defaults(v)
+
+
+def remove_defaults(v, schema):
+    return schema.remove_defaults(v)
+
+
+def load_from_filename(
+        filename,
+        schema,
+        load_strategy,
+        exc_tp=ValidationError,
+):
+    with reraise_as(exc_tp):
+        if not os.path.exists(filename):
+            raise ValidationError(f'{filename} does not exist')
+
+        with open(filename, encoding='utf-8') as f:
+            contents = f.read()
+
+        with validate_context(f'File {filename}'):
+            try:
+                data = load_strategy(contents)
+            except Exception as e:
+                raise ValidationError(str(e))
+
+            validate(data, schema)
+            return apply_defaults(data, schema)
diff --git a/requirements-dev.txt b/requirements-dev.txt
new file mode 100644
index 0000000..4dbfffa
--- /dev/null
+++ b/requirements-dev.txt
@@ -0,0 +1,3 @@
+coverage
+pre-commit
+pytest
diff --git a/setup.cfg b/setup.cfg
new file mode 100644
index 0000000..ce6e897
--- /dev/null
+++ b/setup.cfg
@@ -0,0 +1,27 @@
+[metadata]
+name = cfgv
+version = 3.1.0
+description = Validate configuration and produce human readable error messages.
+long_description = file: README.md
+long_description_content_type = text/markdown
+url = https://github.com/asottile/cfgv
+author = Anthony Sottile
+author_email = asottile@umich.edu
+license = MIT
+license_file = LICENSE
+classifiers =
+    License :: OSI Approved :: MIT License
+    Programming Language :: Python :: 3
+    Programming Language :: Python :: 3 :: Only
+    Programming Language :: Python :: 3.6
+    Programming Language :: Python :: 3.7
+    Programming Language :: Python :: 3.8
+    Programming Language :: Python :: Implementation :: CPython
+    Programming Language :: Python :: Implementation :: PyPy
+
+[options]
+py_modules = cfgv
+python_requires = >=3.6.1
+
+[bdist_wheel]
+universal = True
diff --git a/setup.py b/setup.py
new file mode 100644
index 0000000..8bf1ba9
--- /dev/null
+++ b/setup.py
@@ -0,0 +1,2 @@
+from setuptools import setup
+setup()
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/tests/__init__.py
diff --git a/tests/cfgv_test.py b/tests/cfgv_test.py
new file mode 100644
index 0000000..1b143a6
--- /dev/null
+++ b/tests/cfgv_test.py
@@ -0,0 +1,680 @@
+import json
+from unittest import mock
+
+import pytest
+
+from cfgv import apply_defaults
+from cfgv import Array
+from cfgv import check_and
+from cfgv import check_any
+from cfgv import check_array
+from cfgv import check_bool
+from cfgv import check_one_of
+from cfgv import check_regex
+from cfgv import check_type
+from cfgv import Conditional
+from cfgv import ConditionalOptional
+from cfgv import ConditionalRecurse
+from cfgv import In
+from cfgv import load_from_filename
+from cfgv import Map
+from cfgv import MISSING
+from cfgv import NoAdditionalKeys
+from cfgv import Not
+from cfgv import NotIn
+from cfgv import Optional
+from cfgv import OptionalNoDefault
+from cfgv import OptionalRecurse
+from cfgv import remove_defaults
+from cfgv import Required
+from cfgv import RequiredRecurse
+from cfgv import validate
+from cfgv import ValidationError
+from cfgv import WarnAdditionalKeys
+
+
+def _assert_exception_trace(e, trace):
+    inner = e
+    for ctx in trace[:-1]:
+        assert inner.ctx == ctx
+        inner = inner.error_msg
+    assert inner.error_msg == trace[-1]
+
+
+def test_ValidationError_simple_str():
+    assert str(ValidationError('error msg')) == (
+        '\n'
+        '=====> error msg'
+    )
+
+
+def test_ValidationError_nested():
+    error = ValidationError(
+        ValidationError(
+            ValidationError('error msg'),
+            ctx='At line 1',
+        ),
+        ctx='In file foo',
+    )
+    assert str(error) == (
+        '\n'
+        '==> In file foo\n'
+        '==> At line 1\n'
+        '=====> error msg'
+    )
+
+
+def test_check_one_of():
+    with pytest.raises(ValidationError) as excinfo:
+        check_one_of((1, 2))(3)
+    assert excinfo.value.error_msg == 'Expected one of 1, 2 but got: 3'
+
+
+def test_check_one_of_ok():
+    check_one_of((1, 2))(2)
+
+
+def test_check_regex():
+    with pytest.raises(ValidationError) as excinfo:
+        check_regex('(')
+    assert excinfo.value.error_msg == "'(' is not a valid python regex"
+
+
+def test_check_regex_ok():
+    check_regex('^$')
+
+
+def test_check_array_failed_inner_check():
+    check = check_array(check_bool)
+    with pytest.raises(ValidationError) as excinfo:
+        check([True, False, 5])
+    _assert_exception_trace(
+        excinfo.value, ('At index 2', 'Expected bool got int'),
+    )
+
+
+def test_check_array_ok():
+    check_array(check_bool)([True, False])
+
+
+def test_check_and():
+    check = check_and(check_type(str), check_regex)
+    with pytest.raises(ValidationError) as excinfo:
+        check(True)
+    assert excinfo.value.error_msg == 'Expected str got bool'
+    with pytest.raises(ValidationError) as excinfo:
+        check('(')
+    assert excinfo.value.error_msg == "'(' is not a valid python regex"
+
+
+def test_check_and_ok():
+    check = check_and(check_type(str), check_regex)
+    check('^$')
+
+
+@pytest.mark.parametrize(
+    ('val', 'expected'),
+    (('bar', True), ('foo', False), (MISSING, False)),
+)
+def test_not(val, expected):
+    compared = Not('foo')
+    assert (val == compared) is expected
+    assert (compared == val) is expected
+
+
+@pytest.mark.parametrize(
+    ('values', 'expected'),
+    (('bar', True), ('foo', False), (MISSING, False)),
+)
+def test_not_in(values, expected):
+    compared = NotIn('baz', 'foo')
+    assert (values == compared) is expected
+    assert (compared == values) is expected
+
+
+@pytest.mark.parametrize(
+    ('values', 'expected'),
+    (('bar', False), ('foo', True), ('baz', True), (MISSING, False)),
+)
+def test_in(values, expected):
+    compared = In('baz', 'foo')
+    assert (values == compared) is expected
+    assert (compared == values) is expected
+
+
+trivial_array_schema = Array(Map('foo', 'id'))
+trivial_array_schema_nonempty = Array(Map('foo', 'id'), allow_empty=False)
+
+
+def test_validate_top_level_array_not_an_array():
+    with pytest.raises(ValidationError) as excinfo:
+        validate({}, trivial_array_schema)
+    assert excinfo.value.error_msg == "Expected array but got 'dict'"
+
+
+def test_validate_top_level_array_no_objects():
+    with pytest.raises(ValidationError) as excinfo:
+        validate([], trivial_array_schema_nonempty)
+    assert excinfo.value.error_msg == "Expected at least 1 'foo'"
+
+
+def test_trivial_array_schema_ok_empty():
+    validate([], trivial_array_schema)
+
+
+@pytest.mark.parametrize('v', (({},), [{}]))
+def test_ok_both_types(v):
+    validate(v, trivial_array_schema)
+
+
+map_required = Map('foo', 'key', Required('key', check_bool))
+map_optional = Map('foo', 'key', Optional('key', check_bool, False))
+map_no_default = Map('foo', 'key', OptionalNoDefault('key', check_bool))
+map_no_id_key = Map('foo', None, Required('key', check_bool))
+
+
+def test_map_wrong_type():
+    with pytest.raises(ValidationError) as excinfo:
+        validate([], map_required)
+    assert excinfo.value.error_msg == 'Expected a foo map but got a list'
+
+
+def test_required_missing_key():
+    with pytest.raises(ValidationError) as excinfo:
+        validate({}, map_required)
+    expected = ('At foo(key=MISSING)', 'Missing required key: key')
+    _assert_exception_trace(excinfo.value, expected)
+
+
+@pytest.mark.parametrize(
+    'schema', (map_required, map_optional, map_no_default),
+)
+def test_map_value_wrong_type(schema):
+    with pytest.raises(ValidationError) as excinfo:
+        validate({'key': 5}, schema)
+    expected = ('At foo(key=5)', 'At key: key', 'Expected bool got int')
+    _assert_exception_trace(excinfo.value, expected)
+
+
+@pytest.mark.parametrize(
+    'schema', (map_required, map_optional, map_no_default),
+)
+def test_map_value_correct_type(schema):
+    validate({'key': True}, schema)
+
+
+@pytest.mark.parametrize('schema', (map_optional, map_no_default))
+def test_optional_key_missing(schema):
+    validate({}, schema)
+
+
+def test_error_message_no_id_key():
+    with pytest.raises(ValidationError) as excinfo:
+        validate({'key': 5}, map_no_id_key)
+    expected = ('At foo()', 'At key: key', 'Expected bool got int')
+    _assert_exception_trace(excinfo.value, expected)
+
+
+map_conditional = Map(
+    'foo', 'key',
+    Conditional(
+        'key2', check_bool, condition_key='key', condition_value=True,
+    ),
+)
+map_conditional_not = Map(
+    'foo', 'key',
+    Conditional(
+        'key2', check_bool, condition_key='key', condition_value=Not(False),
+    ),
+)
+map_conditional_absent = Map(
+    'foo', 'key',
+    Conditional(
+        'key2', check_bool,
+        condition_key='key', condition_value=True, ensure_absent=True,
+    ),
+)
+map_conditional_absent_not = Map(
+    'foo', 'key',
+    Conditional(
+        'key2', check_bool,
+        condition_key='key', condition_value=Not(True), ensure_absent=True,
+    ),
+)
+map_conditional_absent_not_in = Map(
+    'foo', 'key',
+    Conditional(
+        'key2', check_bool,
+        condition_key='key', condition_value=NotIn(1, 2), ensure_absent=True,
+    ),
+)
+map_conditional_absent_in = Map(
+    'foo', 'key',
+    Conditional(
+        'key2', check_bool,
+        condition_key='key', condition_value=In(1, 2), ensure_absent=True,
+    ),
+)
+
+
+@pytest.mark.parametrize('schema', (map_conditional, map_conditional_not))
+@pytest.mark.parametrize(
+    'v',
+    (
+        # Conditional check passes, key2 is checked and passes
+        {'key': True, 'key2': True},
+        # Conditional check fails, key2 is not checked
+        {'key': False, 'key2': 'ohai'},
+    ),
+)
+def test_ok_conditional_schemas(v, schema):
+    validate(v, schema)
+
+
+@pytest.mark.parametrize('schema', (map_conditional, map_conditional_not))
+def test_not_ok_conditional_schemas(schema):
+    with pytest.raises(ValidationError) as excinfo:
+        validate({'key': True, 'key2': 5}, schema)
+    expected = ('At foo(key=True)', 'At key: key2', 'Expected bool got int')
+    _assert_exception_trace(excinfo.value, expected)
+
+
+def test_ensure_absent_conditional():
+    with pytest.raises(ValidationError) as excinfo:
+        validate({'key': False, 'key2': True}, map_conditional_absent)
+    expected = (
+        'At foo(key=False)',
+        'Expected key2 to be absent when key is not True, '
+        'found key2: True',
+    )
+    _assert_exception_trace(excinfo.value, expected)
+
+
+def test_ensure_absent_conditional_not():
+    with pytest.raises(ValidationError) as excinfo:
+        validate({'key': True, 'key2': True}, map_conditional_absent_not)
+    expected = (
+        'At foo(key=True)',
+        'Expected key2 to be absent when key is True, '
+        'found key2: True',
+    )
+    _assert_exception_trace(excinfo.value, expected)
+
+
+def test_ensure_absent_conditional_not_in():
+    with pytest.raises(ValidationError) as excinfo:
+        validate({'key': 1, 'key2': True}, map_conditional_absent_not_in)
+    expected = (
+        'At foo(key=1)',
+        'Expected key2 to be absent when key is any of (1, 2), '
+        'found key2: True',
+    )
+    _assert_exception_trace(excinfo.value, expected)
+
+
+def test_ensure_absent_conditional_in():
+    with pytest.raises(ValidationError) as excinfo:
+        validate({'key': 3, 'key2': True}, map_conditional_absent_in)
+    expected = (
+        'At foo(key=3)',
+        'Expected key2 to be absent when key is not any of (1, 2), '
+        'found key2: True',
+    )
+    _assert_exception_trace(excinfo.value, expected)
+
+
+def test_no_error_conditional_absent():
+    validate({}, map_conditional_absent)
+    validate({}, map_conditional_absent_not)
+    validate({'key2': True}, map_conditional_absent)
+    validate({'key2': True}, map_conditional_absent_not)
+
+
+def test_apply_defaults_copies_object():
+    val = {}
+    ret = apply_defaults(val, map_optional)
+    assert ret is not val
+
+
+def test_apply_defaults_sets_default():
+    ret = apply_defaults({}, map_optional)
+    assert ret == {'key': False}
+
+
+def test_apply_defaults_does_not_change_non_default():
+    ret = apply_defaults({'key': True}, map_optional)
+    assert ret == {'key': True}
+
+
+def test_apply_defaults_does_nothing_on_non_optional():
+    ret = apply_defaults({}, map_required)
+    assert ret == {}
+
+
+def test_apply_defaults_map_in_list():
+    ret = apply_defaults([{}], Array(map_optional))
+    assert ret == [{'key': False}]
+
+
+def test_remove_defaults_copies_object():
+    val = {'key': False}
+    ret = remove_defaults(val, map_optional)
+    assert ret is not val
+
+
+def test_remove_defaults_removes_defaults():
+    ret = remove_defaults({'key': False}, map_optional)
+    assert ret == {}
+
+
+def test_remove_defaults_nothing_to_remove():
+    ret = remove_defaults({}, map_optional)
+    assert ret == {}
+
+
+def test_remove_defaults_does_not_change_non_default():
+    ret = remove_defaults({'key': True}, map_optional)
+    assert ret == {'key': True}
+
+
+def test_remove_defaults_map_in_list():
+    ret = remove_defaults([{'key': False}], Array(map_optional))
+    assert ret == [{}]
+
+
+def test_remove_defaults_does_nothing_on_non_optional():
+    ret = remove_defaults({'key': True}, map_required)
+    assert ret == {'key': True}
+
+
+nested_schema_required = Map(
+    'Repository', 'repo',
+    Required('repo', check_any),
+    RequiredRecurse('hooks', Array(map_required)),
+)
+nested_schema_optional = Map(
+    'Repository', 'repo',
+    Required('repo', check_any),
+    RequiredRecurse('hooks', Array(map_optional)),
+)
+
+
+def test_validate_failure_nested():
+    with pytest.raises(ValidationError) as excinfo:
+        validate({'repo': 1, 'hooks': [{}]}, nested_schema_required)
+    expected = (
+        'At Repository(repo=1)',
+        'At key: hooks',
+        'At foo(key=MISSING)',
+        'Missing required key: key',
+    )
+    _assert_exception_trace(excinfo.value, expected)
+
+
+def test_apply_defaults_nested():
+    val = {'repo': 'repo1', 'hooks': [{}]}
+    ret = apply_defaults(val, nested_schema_optional)
+    assert ret == {'repo': 'repo1', 'hooks': [{'key': False}]}
+
+
+def test_remove_defaults_nested():
+    val = {'repo': 'repo1', 'hooks': [{'key': False}]}
+    ret = remove_defaults(val, nested_schema_optional)
+    assert ret == {'repo': 'repo1', 'hooks': [{}]}
+
+
+link = Map('Link', 'key', Required('key', check_bool))
+optional_nested_schema = Map(
+    'Config', None,
+    OptionalRecurse('links', Array(link), []),
+)
+
+
+def test_validate_failure_optional_recurse():
+    with pytest.raises(ValidationError) as excinfo:
+        validate({'links': [{}]}, optional_nested_schema)
+    expected = (
+        'At Config()',
+        'At key: links',
+        'At Link(key=MISSING)',
+        'Missing required key: key',
+    )
+    _assert_exception_trace(excinfo.value, expected)
+
+
+def test_optional_recurse_ok_missing():
+    validate({}, optional_nested_schema)
+
+
+def test_apply_defaults_optional_recurse_missing():
+    ret = apply_defaults({}, optional_nested_schema)
+    assert ret == {'links': []}
+
+
+def test_apply_defaults_optional_recurse_already_present():
+    ret = apply_defaults({'links': [{'key': True}]}, optional_nested_schema)
+    assert ret == {'links': [{'key': True}]}
+
+
+def test_remove_defaults_optional_recurse_not_present():
+    assert remove_defaults({}, optional_nested_schema) == {}
+
+
+def test_remove_defaults_optional_recurse_present_at_default():
+    assert remove_defaults({'links': []}, optional_nested_schema) == {}
+
+
+def test_remove_defaults_optional_recurse_non_default():
+    ret = remove_defaults({'links': [{'key': True}]}, optional_nested_schema)
+    assert ret == {'links': [{'key': True}]}
+
+
+builder_opts = Map('BuilderOpts', None, Optional('noop', check_bool, True))
+optional_nested_optional_schema = Map(
+    'Config', None,
+    OptionalRecurse('builder', builder_opts, {}),
+)
+
+
+def test_optional_optional_apply_defaults():
+    ret = apply_defaults({}, optional_nested_optional_schema)
+    assert ret == {'builder': {'noop': True}}
+
+
+def test_optional_optional_remove_defaults():
+    val = {'builder': {'noop': True}}
+    ret = remove_defaults(val, optional_nested_optional_schema)
+    assert ret == {}
+
+
+params1_schema = Map('Params1', None, Required('p1', check_bool))
+params2_schema = Map('Params2', None, Required('p2', check_bool))
+conditional_nested_schema = Map(
+    'Config', None,
+    Required('type', check_any),
+    ConditionalRecurse('params', params1_schema, 'type', 'type1'),
+    ConditionalRecurse('params', params2_schema, 'type', 'type2'),
+)
+
+
+@pytest.mark.parametrize(
+    'val',
+    (
+        {'type': 'type3'},  # matches no condition
+        {'type': 'type1', 'params': {'p1': True}},
+        {'type': 'type2', 'params': {'p2': True}},
+    ),
+)
+def test_conditional_recurse_ok(val):
+    validate(val, conditional_nested_schema)
+
+
+def test_conditional_recurse_error():
+    with pytest.raises(ValidationError) as excinfo:
+        val = {'type': 'type1', 'params': {'p2': True}}
+        validate(val, conditional_nested_schema)
+    expected = (
+        'At Config()',
+        'At key: params',
+        'At Params1()',
+        'Missing required key: p1',
+    )
+    _assert_exception_trace(excinfo.value, expected)
+
+
+class Error(Exception):
+    pass
+
+
+def test_load_from_filename_file_does_not_exist():
+    with pytest.raises(Error) as excinfo:
+        load_from_filename('does_not_exist', map_required, json.loads, Error)
+    assert excinfo.value.args[0].error_msg == 'does_not_exist does not exist'
+
+
+def test_load_from_filename_fails_load_strategy(tmpdir):
+    f = tmpdir.join('foo.notjson')
+    f.write('totes not json')
+    with pytest.raises(Error) as excinfo:
+        load_from_filename(f.strpath, map_required, json.loads, Error)
+    # ANY is json's error message
+    expected = (f'File {f.strpath}', mock.ANY)
+    _assert_exception_trace(excinfo.value.args[0], expected)
+
+
+def test_load_from_filename_validation_error(tmpdir):
+    f = tmpdir.join('foo.json')
+    f.write('{}')
+    with pytest.raises(Error) as excinfo:
+        load_from_filename(f.strpath, map_required, json.loads, Error)
+    expected = (
+        f'File {f.strpath}',
+        'At foo(key=MISSING)',
+        'Missing required key: key',
+    )
+    _assert_exception_trace(excinfo.value.args[0], expected)
+
+
+def test_load_from_filename_applies_defaults(tmpdir):
+    f = tmpdir.join('foo.json')
+    f.write('{}')
+    ret = load_from_filename(f.strpath, map_optional, json.loads, Error)
+    assert ret == {'key': False}
+
+
+conditional_recurse = Map(
+    'Map', None,
+
+    Required('t', check_bool),
+    ConditionalRecurse(
+        'v', Map('Inner', 'k', Optional('k', check_bool, True)),
+        't', True,
+    ),
+    ConditionalRecurse(
+        'v', Map('Inner', 'k', Optional('k', check_bool, False)),
+        't', False,
+    ),
+)
+
+
+@pytest.mark.parametrize('tvalue', (True, False))
+def test_conditional_recurse_apply_defaults(tvalue):
+    val = {'t': tvalue, 'v': {}}
+    ret = apply_defaults(val, conditional_recurse)
+    assert ret == {'t': tvalue, 'v': {'k': tvalue}}
+
+    val = {'t': tvalue, 'v': {'k': not tvalue}}
+    ret = apply_defaults(val, conditional_recurse)
+    assert ret == {'t': tvalue, 'v': {'k': not tvalue}}
+
+
+@pytest.mark.parametrize('tvalue', (True, False))
+def test_conditional_recurse_remove_defaults(tvalue):
+    val = {'t': tvalue, 'v': {'k': tvalue}}
+    ret = remove_defaults(val, conditional_recurse)
+    assert ret == {'t': tvalue, 'v': {}}
+
+    val = {'t': tvalue, 'v': {'k': not tvalue}}
+    ret = remove_defaults(val, conditional_recurse)
+    assert ret == {'t': tvalue, 'v': {'k': not tvalue}}
+
+
+conditional_optional = Map(
+    'Map', None,
+
+    Required('t', check_bool),
+    ConditionalOptional('v', check_bool, True, 't', True),
+    ConditionalOptional('v', check_bool, False, 't', False),
+)
+
+
+@pytest.mark.parametrize('tvalue', (True, False))
+def test_conditional_optional_check(tvalue):
+    with pytest.raises(ValidationError) as excinfo:
+        validate({'t': tvalue, 'v': 2}, conditional_optional)
+    expected = (
+        'At Map()',
+        'At key: v',
+        'Expected bool got int',
+    )
+    _assert_exception_trace(excinfo.value, expected)
+
+    validate({'t': tvalue, 'v': tvalue}, conditional_optional)
+
+
+@pytest.mark.parametrize('tvalue', (True, False))
+def test_conditional_optional_apply_default(tvalue):
+    ret = apply_defaults({'t': tvalue}, conditional_optional)
+    assert ret == {'t': tvalue, 'v': tvalue}
+
+
+@pytest.mark.parametrize('tvalue', (True, False))
+def test_conditional_optional_remove_default(tvalue):
+    ret = remove_defaults({'t': tvalue, 'v': tvalue}, conditional_optional)
+    assert ret == {'t': tvalue}
+    ret = remove_defaults({'t': tvalue, 'v': not tvalue}, conditional_optional)
+    assert ret == {'t': tvalue, 'v': not tvalue}
+
+
+no_additional_keys = Map(
+    'Map', None,
+    Required(True, check_bool),
+    NoAdditionalKeys((True,)),
+)
+
+
+def test_no_additional_keys():
+    with pytest.raises(ValidationError) as excinfo:
+        validate({True: True, False: False}, no_additional_keys)
+    expected = (
+        'At Map()',
+        'Additional keys found: False.  Only these keys are allowed: True',
+    )
+    _assert_exception_trace(excinfo.value, expected)
+
+    validate({True: True}, no_additional_keys)
+
+
+@pytest.fixture
+def warn_additional_keys():
+    ret = mock.Mock()
+
+    def callback(extra, keys, dct):
+        return ret.record(extra, keys, dct)
+
+    ret.schema = Map(
+        'Map', None,
+        Required(True, check_bool),
+        WarnAdditionalKeys((True,), callback),
+    )
+    yield ret
+
+
+def test_warn_additional_keys_when_has_extra_keys(warn_additional_keys):
+    validate({True: True, False: False}, warn_additional_keys.schema)
+    assert warn_additional_keys.record.called
+
+
+def test_warn_additional_keys_when_no_extra_keys(warn_additional_keys):
+    validate({True: True}, warn_additional_keys.schema)
+    assert not warn_additional_keys.record.called
diff --git a/tox.ini b/tox.ini
new file mode 100644
index 0000000..3b6f4d7
--- /dev/null
+++ b/tox.ini
@@ -0,0 +1,18 @@
+[tox]
+envlist = py36,py37,pypy3,pre-commit
+
+[testenv]
+deps = -rrequirements-dev.txt
+commands =
+    coverage erase
+    coverage run -m pytest {posargs:tests}
+    coverage report --fail-under 100
+    pre-commit install
+
+[testenv:pre-commit]
+skip_install = true
+deps = pre-commit
+commands = pre-commit run --all-files --show-diff-on-failure
+
+[pep8]
+ignore = E265,E501,W504