Reuse parent collection for explicit file arguments

AUTHORS

@@ -212,6 +212,7 @@ Harshna
 Henk-Jaap Wagenaar
 Henry Schreiner
 Holger Kohr
+Huashuo Lei
 Hugo van Kemenade
 Hui Wang (coldnight)
 Ian Bicking

changelog/15251.bugfix.rst

@@ -0,0 +1 @@
+Reused a parent directory's collection results when multiple test files from that directory are supplied as explicit command-line arguments.

src/_pytest/main.py

@@ -990,10 +990,13 @@ def collect(self) -> Iterator[nodes.Item | nodes.Collector]:
                     assert isinstance(matchparts[0], Path)
                     subnodes = matchnode._collect_path(matchparts[0], path_cache)
                 else:
-                    # For backward compat, files given directly multiple
-                    # times on the command line should not be deduplicated.
+                    # A file argument reaches this collector as its final path
+                    # part, but this is still the parent directory. Reuse the
+                    # cached collection unless --keep-duplicates needs a fresh
+                    # parent collection for an overlapping file argument.
                     handle_dupes = not (
-                        len(matchparts) == 1
+                        self.config.getoption("keepduplicates")
+                        and len(matchparts) == 1
                         and isinstance(matchparts[0], Path)
                         and matchparts[0].is_file()
                     )

testing/test_collection.py

@@ -2142,6 +2142,35 @@ def test_a(): pass
             consecutive=True,
         )
 
+    def test_explicit_file_arguments_collect_shared_directory_once(
+        self, pytester: Pytester
+    ) -> None:
+        files = {f"tests/test_{i}.py": "def test_example(): pass" for i in range(8)}
+        pytester.makepyfile(**files)
+        pytester.makeconftest(
+            """
+            from collections import Counter
+            from pathlib import Path
+
+            collected = Counter()
+
+            def pytest_collect_file(file_path, parent):
+                if file_path.name.startswith("test_"):
+                    collected[file_path.name] += 1
+
+            def pytest_sessionfinish(session, exitstatus):
+                Path("collect-counts.txt").write_text(str(sum(collected.values())), encoding="utf-8")
+            """
+        )
+
+        file_args = [f"tests/test_{i}.py" for i in range(4)]
+        result = pytester.runpytest_subprocess("--collect-only", *file_args)
+
+        assert result.ret == ExitCode.OK
+        assert int(
+            pytester.path.joinpath("collect-counts.txt").read_text(encoding="utf-8")
+        ) == len(files)
+
     def test_keep_duplicates_flag(self, pytester: Pytester) -> None:
         """Test that --keep-duplicates allows duplication."""
         pytester.makepyfile(