Test .gitignore with */* is applied correctly

The test contains three cases: 1) when the .gitignore with the special
rule to ignore every subfolder and its contents (*/*) is in the root,
2) when the file is inside a subfolder relative to root (nested), and
3) when the target folder contains the .gitignore and root is a parent
folder of the target. In all of these cases, we compare the files that
are visible by Black with a known list of paths containing the
expected values.

Before the fix introduced in the previous commit, these tests failed
when the .gitignore file was nested (second case). Now, the test is
passed for all cases.

Signed-off-by: Antonio Ossa Guerra <aaossa@uc.cl>

tests/data/ignore_subfolders_gitignore_tests/subdir/.gitignore

@@ -0,0 +1 @@
+*/*

tests/test_black.py

@@ -2056,6 +2056,32 @@ def test_invalid_nested_gitignore(self) -> None:
         gitignore = path / "a" / ".gitignore"
         assert f"Could not parse {gitignore}" in result.stderr_bytes.decode()
 
+    def test_gitignore_that_ignores_subfolders(self) -> None:
+        # If gitignore with */* is in root
+        root = Path(DATA_DIR / "ignore_subfolders_gitignore_tests" / "subdir")
+        expected = [root / "b.py"]
+        ctx = FakeContext()
+        ctx.obj["root"] = root
+        assert_collected_sources([root], expected, ctx=ctx)
+
+        # If .gitignore with */* is nested
+        root = Path(DATA_DIR / "ignore_subfolders_gitignore_tests")
+        expected = [
+            root / "a.py",
+            root / "subdir" / "b.py",
+        ]
+        ctx = FakeContext()
+        ctx.obj["root"] = root
+        assert_collected_sources([root], expected, ctx=ctx)
+
+        # If command is executed from outer dir
+        root = Path(DATA_DIR / "ignore_subfolders_gitignore_tests")
+        target = root / "subdir"
+        expected = [target / "b.py"]
+        ctx = FakeContext()
+        ctx.obj["root"] = root
+        assert_collected_sources([target], expected, ctx=ctx)
+
     def test_empty_include(self) -> None:
         path = DATA_DIR / "include_exclude_tests"
         src = [path]