1 files changed, 71 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/tests_outside_test_module.rs b/src/tools/clippy/clippy_lints/src/tests_outside_test_module.rs
new file mode 100644
index 000000000..0a0a77082
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/tests_outside_test_module.rs
@@ -0,0 +1,71 @@
+use clippy_utils::{diagnostics::span_lint_and_note, is_in_cfg_test, is_in_test_function};
+use rustc_hir::{intravisit::FnKind, Body, FnDecl};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::{def_id::LocalDefId, Span};
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Triggers when a testing function (marked with the `#[test]` attribute) isn't inside a testing module
+    /// (marked with `#[cfg(test)]`).
+    /// ### Why is this bad?
+    /// The idiomatic (and more performant) way of writing tests is inside a testing module (flagged with `#[cfg(test)]`),
+    /// having test functions outside of this module is confusing and may lead to them being "hidden".
+    /// ### Example
+    /// ```rust
+    /// #[test]
+    /// fn my_cool_test() {
+    ///     // [...]
+    /// }
+    ///
+    /// #[cfg(test)]
+    /// mod tests {
+    ///     // [...]
+    /// }
+    ///
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// #[cfg(test)]
+    /// mod tests {
+    ///     #[test]
+    ///     fn my_cool_test() {
+    ///         // [...]
+    ///     }
+    /// }
+    /// ```
+    #[clippy::version = "1.70.0"]
+    pub TESTS_OUTSIDE_TEST_MODULE,
+    restriction,
+    "A test function is outside the testing module."
+}
+
+declare_lint_pass!(TestsOutsideTestModule => [TESTS_OUTSIDE_TEST_MODULE]);
+
+impl LateLintPass<'_> for TestsOutsideTestModule {
+    fn check_fn(
+        &mut self,
+        cx: &LateContext<'_>,
+        kind: FnKind<'_>,
+        _: &FnDecl<'_>,
+        body: &Body<'_>,
+        sp: Span,
+        _: LocalDefId,
+    ) {
+        if_chain! {
+            if !matches!(kind, FnKind::Closure);
+            if is_in_test_function(cx.tcx, body.id().hir_id);
+            if !is_in_cfg_test(cx.tcx, body.id().hir_id);
+            then {
+                span_lint_and_note(
+                    cx,
+                    TESTS_OUTSIDE_TEST_MODULE,
+                    sp,
+                    "this function marked with #[test] is outside a #[cfg(test)] module",
+                    None,
+                    "move it to a testing module marked with #[cfg(test)]",
+                );
+            }
+        }
+    }
+}