Choose distinct debug adapter ports in different tests. (#17837)

Prevents a port collision error if the two test files happen
to run concurrently.

pants.toml

@@ -175,6 +175,7 @@ extra_requirements.add = [
   "pygments",
 ]
 lockfile = "3rdparty/python/pytest.lock"
+execution_slot_var = "TEST_EXECUTION_SLOT"
 
 [test]
 extra_env_vars = [

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

@@ -48,6 +48,7 @@
 from pants.engine.rules import Get, rule
 from pants.engine.target import Target
 from pants.engine.unions import UnionRule
+from pants.testutil.debug_adapter_util import debugadapter_port_for_testing
 from pants.testutil.python_interpreter_selection import (
     all_major_minor_python_versions,
     skip_unless_python27_and_python3_present,
@@ -108,6 +109,7 @@ def _configure_pytest_runner(
     args = [
         "--backend-packages=pants.backend.python",
         f"--source-root-patterns={SOURCE_ROOT}",
+        f"--debug-adapter-port={debugadapter_port_for_testing()}",
         *(extra_args or ()),
     ]
     rule_runner.set_options(args, env=env, env_inherit={"PATH", "PYENV_ROOT", "HOME"})

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

@@ -37,6 +37,7 @@
 from pants.engine.process import InteractiveProcess
 from pants.engine.rules import QueryRule
 from pants.engine.target import Target
+from pants.testutil.debug_adapter_util import debugadapter_port_for_testing
 from pants.testutil.pants_integration_test import run_pants
 from pants.testutil.rule_runner import RuleRunner, mock_console
 
@@ -186,6 +187,7 @@ def my_file():
         "--backend-packages=pants.backend.python",
         "--backend-packages=pants.backend.codegen.protobuf.python",
         "--source-root-patterns=['src_root1', 'src_root2']",
+        f"--debug-adapter-port={debugadapter_port_for_testing()}",
         *(
             (
                 "--python-default-run-goal-use-sandbox"

src/python/pants/testutil/debug_adapter_util.py

@@ -0,0 +1,16 @@
+# Copyright 2022 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+import os
+
+
+def debugadapter_port_for_testing() -> int:
+    """Return a unique-per-concurrent-process debug adapter port.
+
+    Use this in Pants's (and plugins') own tests to avoid collisions.
+
+    Assumes that the env var TEST_EXECUTION_SLOT has been set. If not, all tests
+    will use the same port, and collisions may occur.
+    """
+    execution_slot = os.environ.get("TEST_EXECUTION_SLOT", "0")
+    return 22000 + int(execution_slot)