drop python3.9 specific tests that use the bundled lockfiles

I think these "does black/mypy support Python syntax circa 2020?"
tests have outlived their usefulness and removing them makes it easier
to drop support for Python 3.9 (EoL since 2025-10-31).

There are still tests that use 3.8 when custom test lockfiles when
available, which cover the "Does Pants work with Pythons older than
the bundled tool lockfiles?" case.

Author: cburroughs

src/python/pants/backend/python/goals/lockfile_test.py

@@ -717,7 +717,7 @@ def test_uv_lockfile_generation(
     metadata = json.loads(by_path["test.lock.metadata"].content.decode())
     assert metadata["version"] == 8
     assert metadata["lockfile_format"] == LockfileFormat.UV
-    assert metadata["valid_for_interpreter_constraints"] == ["CPython<3.15,>=3.9"]
+    assert metadata["valid_for_interpreter_constraints"] == ["CPython<3.15,>=3.10"]
     assert metadata["generated_with_requirements"] == [
         "ansicolors==1.1.8",
         "cowsay@ git+https://github.com/VaasuDevanS/cowsay-python@dcf7236f0b5ece9ed56e91271486e560526049cf",

src/python/pants/backend/python/lint/black/rules_integration_test.py

@@ -21,7 +21,6 @@
 from pants.testutil.python_interpreter_selection import (
     all_major_minor_python_versions,
     skip_unless_python38_present,
-    skip_unless_python39_present,
 )
 from pants.testutil.python_rule_runner import PythonRuleRunner
 from pants.testutil.rule_runner import QueryRule
@@ -236,27 +235,6 @@ class Foo:
     assert fmt_result.did_change is False
 
 
-@skip_unless_python39_present
-def test_works_with_python39(rule_runner: PythonRuleRunner) -> None:
-    """Black's typed-ast dependency does not understand Python 3.9, so we must instead run Black
-    with Python 3.9 when relevant."""
-    content = dedent(
-        """\
-        @lambda _: int
-        def replaced(x: bool) -> str:
-            return "42" if x is True else "1/137"
-        """
-    )
-    rule_runner.write_files(
-        {"f.py": content, "BUILD": "python_sources(name='t', interpreter_constraints=['>=3.9'])"}
-    )
-    tgt = rule_runner.get_target(Address("", target_name="t", relative_file_path="f.py"))
-    fmt_result = run_black(rule_runner, [tgt], expected_ics=">=3.9")
-    assert "1 file left unchanged" in fmt_result.stderr
-    assert fmt_result.output == rule_runner.make_snapshot({"f.py": content})
-    assert fmt_result.did_change is False
-
-
 def test_stub_files(rule_runner: PythonRuleRunner) -> None:
     rule_runner.write_files(
         {

src/python/pants/backend/python/typecheck/mypy/rules_integration_test.py

@@ -42,7 +42,6 @@
     all_major_minor_python_versions,
     skip_unless_all_pythons_present,
     skip_unless_python38_present,
-    skip_unless_python39_present,
 )
 from pants.testutil.python_rule_runner import PythonRuleRunner
 from pants.util.resources import read_sibling_resource
@@ -357,26 +356,6 @@ def test_works_with_python38(rule_runner: PythonRuleRunner) -> None:
     assert_success(rule_runner, tgt, extra_args=extra_args)
 
 
-@skip_unless_python39_present
-def test_works_with_python39(rule_runner: PythonRuleRunner) -> None:
-    """MyPy's typed-ast dependency does not understand Python 3.9, so we must instead run MyPy with
-    Python 3.9 when relevant."""
-    rule_runner.write_files(
-        {
-            f"{PACKAGE}/f.py": dedent(
-                """\
-                @lambda _: int
-                def replaced(x: bool) -> str:
-                    return "42" if x is True else "1/137"
-                """
-            ),
-            f"{PACKAGE}/BUILD": "python_sources(interpreter_constraints=['>=3.9'])",
-        }
-    )
-    tgt = rule_runner.get_target(Address(PACKAGE, relative_file_path="f.py"))
-    assert_success(rule_runner, tgt)
-
-
 def test_run_only_on_specified_files(rule_runner: PythonRuleRunner) -> None:
     rule_runner.write_files(
         {

src/python/pants/base/specs_integration_test.py

@@ -7,7 +7,7 @@
 from textwrap import dedent
 
 from pants.testutil.pants_integration_test import PantsResult, run_pants, setup_tmpdir
-from pants.testutil.python_interpreter_selection import skip_unless_python39_present
+from pants.testutil.python_interpreter_selection import skip_unless_python310_present
 
 SOURCES = {
     # NB: This uses recursive globs for the `python_sources` and `python_tests` target generators,
@@ -65,7 +65,7 @@ def run(args: list[str]) -> PantsResult:
         [
             "--backend-packages=pants.backend.python",
             "--backend-packages=pants.backend.experimental.go",
-            "--python-interpreter-constraints=['==3.9.*']",
+            "--python-interpreter-constraints=['==3.10.*']",
             "--pants-ignore=__pycache__",
             *args,
         ]
@@ -74,7 +74,7 @@ def run(args: list[str]) -> PantsResult:
     return result
 
 
-@skip_unless_python39_present
+@skip_unless_python310_present
 def test_address_literal() -> None:
     """Semantics:
 
@@ -91,7 +91,7 @@ def test_address_literal() -> None:
         assert f"{tmpdir}/py:tests" not in test_result
 
 
-@skip_unless_python39_present
+@skip_unless_python310_present
 def test_sibling_addresses() -> None:
     """Semantics:
 
@@ -127,7 +127,7 @@ def test_sibling_addresses() -> None:
         assert f"{tmpdir}/py:tests" not in test_result
 
 
-@skip_unless_python39_present
+@skip_unless_python310_present
 def test_descendent_addresses() -> None:
     """Semantics are the same as sibling addresses, only recursive."""
     with setup_tmpdir(SOURCES) as tmpdir:
@@ -148,7 +148,7 @@ def test_descendent_addresses() -> None:
         assert f"{tmpdir}/py:tests" not in test_result
 
 
-@skip_unless_python39_present
+@skip_unless_python310_present
 def test_file_arg() -> None:
     """Semantics: find the 'owning' target, using generated target rather than target generator
     when possible (regardless of project introspection vs. "build" goal).