1 files changed, 137 insertions, 0 deletions
diff --git a/tests/test_diff.py b/tests/test_diff.py
new file mode 100644
index 0000000..cbd53b3
--- /dev/null
+++ b/tests/test_diff.py
@@ -0,0 +1,137 @@
+import unittest
+
+from sqlglot import parse_one
+from sqlglot.diff import Insert, Keep, Move, Remove, Update, diff
+from sqlglot.expressions import Join, to_identifier
+
+
+class TestDiff(unittest.TestCase):
+    def test_simple(self):
+        self._validate_delta_only(
+            diff(parse_one("SELECT a + b"), parse_one("SELECT a - b")),
+            [
+                Remove(parse_one("a + b")),  # the Add node
+                Insert(parse_one("a - b")),  # the Sub node
+            ],
+        )
+
+        self._validate_delta_only(
+            diff(parse_one("SELECT a, b, c"), parse_one("SELECT a, c")),
+            [
+                Remove(to_identifier("b", quoted=False)),  # the Identifier node
+                Remove(parse_one("b")),  # the Column node
+            ],
+        )
+
+        self._validate_delta_only(
+            diff(parse_one("SELECT a, b"), parse_one("SELECT a, b, c")),
+            [
+                Insert(to_identifier("c", quoted=False)),  # the Identifier node
+                Insert(parse_one("c")),  # the Column node
+            ],
+        )
+
+        self._validate_delta_only(
+            diff(
+                parse_one("SELECT a FROM table_one"),
+                parse_one("SELECT a FROM table_two"),
+            ),
+            [
+                Update(
+                    to_identifier("table_one", quoted=False),
+                    to_identifier("table_two", quoted=False),
+                ),  # the Identifier node
+            ],
+        )
+
+    def test_node_position_changed(self):
+        self._validate_delta_only(
+            diff(parse_one("SELECT a, b, c"), parse_one("SELECT c, a, b")),
+            [
+                Move(parse_one("c")),  # the Column node
+            ],
+        )
+
+        self._validate_delta_only(
+            diff(parse_one("SELECT a + b"), parse_one("SELECT b + a")),
+            [
+                Move(parse_one("a")),  # the Column node
+            ],
+        )
+
+        self._validate_delta_only(
+            diff(parse_one("SELECT aaaa AND bbbb"), parse_one("SELECT bbbb AND aaaa")),
+            [
+                Move(parse_one("aaaa")),  # the Column node
+            ],
+        )
+
+        self._validate_delta_only(
+            diff(
+                parse_one("SELECT aaaa OR bbbb OR cccc"),
+                parse_one("SELECT cccc OR bbbb OR aaaa"),
+            ),
+            [
+                Move(parse_one("aaaa")),  # the Column node
+                Move(parse_one("cccc")),  # the Column node
+            ],
+        )
+
+    def test_cte(self):
+        expr_src = """
+            WITH
+                cte1 AS (SELECT a, b, LOWER(c) AS c FROM table_one WHERE d = 'filter'),
+                cte2 AS (SELECT d, e, f FROM table_two)
+            SELECT a, b, d, e FROM cte1 JOIN cte2 ON f = c
+        """
+        expr_tgt = """
+            WITH
+                cte1 AS (SELECT a, b, c FROM table_one WHERE d = 'different_filter'),
+                cte2 AS (SELECT d, e, f FROM table_two)
+            SELECT a, b, d, e FROM cte1 JOIN cte2 ON f = c
+        """
+
+        self._validate_delta_only(
+            diff(parse_one(expr_src), parse_one(expr_tgt)),
+            [
+                Remove(parse_one("LOWER(c) AS c")),  # the Alias node
+                Remove(to_identifier("c", quoted=False)),  # the Identifier node
+                Remove(parse_one("LOWER(c)")),  # the Lower node
+                Remove(parse_one("'filter'")),  # the Literal node
+                Insert(parse_one("'different_filter'")),  # the Literal node
+            ],
+        )
+
+    def test_join(self):
+        expr_src = "SELECT a, b FROM t1 LEFT JOIN t2 ON t1.key = t2.key"
+        expr_tgt = "SELECT a, b FROM t1 RIGHT JOIN t2 ON t1.key = t2.key"
+
+        changes = diff(parse_one(expr_src), parse_one(expr_tgt))
+        changes = _delta_only(changes)
+
+        self.assertEqual(len(changes), 2)
+        self.assertTrue(isinstance(changes[0], Remove))
+        self.assertTrue(isinstance(changes[1], Insert))
+        self.assertTrue(all(isinstance(c.expression, Join) for c in changes))
+
+    def test_window_functions(self):
+        expr_src = parse_one("SELECT ROW_NUMBER() OVER (PARTITION BY a ORDER BY b)")
+        expr_tgt = parse_one("SELECT RANK() OVER (PARTITION BY a ORDER BY b)")
+
+        self._validate_delta_only(diff(expr_src, expr_src), [])
+
+        self._validate_delta_only(
+            diff(expr_src, expr_tgt),
+            [
+                Remove(parse_one("ROW_NUMBER()")),  # the Anonymous node
+                Insert(parse_one("RANK()")),  # the Anonymous node
+            ],
+        )
+
+    def _validate_delta_only(self, actual_diff, expected_delta):
+        actual_delta = _delta_only(actual_diff)
+        self.assertEqual(set(actual_delta), set(expected_delta))
+
+
+def _delta_only(changes):
+    return [d for d in changes if not isinstance(d, Keep)]