Refactor test_leaks to drop dead code (#1136)

Author: asvetlov

.codecov.yml

@@ -40,7 +40,7 @@ coverage:
       typing:
         flags:
         - MyPy
-        target: 85%
+        target: 80%
 
 github_checks:
   annotations: false

tests/test_leaks.py

@@ -23,15 +23,9 @@ def test_leak(script: str) -> None:
     """Run isolated leak test script and check for leaks."""
     leak_test_script = pathlib.Path(__file__).parent.joinpath("isolated", script)
 
-    with subprocess.Popen(
+    subprocess.run(
         [sys.executable, "-u", str(leak_test_script)],
         stdout=subprocess.PIPE,
         stderr=subprocess.PIPE,
-    ) as proc:
-        exit_code = proc.wait()
-        if exit_code != 0:
-            outs, errs = proc.communicate()
-            raise AssertionError(
-                f"Process exited with code {exit_code}, "
-                f"stdout: {outs!r}, stderr: {errs!r}"
-            )
+        check=True,
+    )