Make expect_stderr mean the weaker allow_stderr_warning.

tests/functional/test_install.py

@@ -1474,8 +1474,7 @@ def test_install_conflict_results_in_warning(script, data):
 
     # Then install an incorrect version of the dependency
     result2 = script.pip(
-        'install', '--no-index', pkgB_path,
-        expect_stderr=True,
+        'install', '--no-index', pkgB_path, allow_stderr_error=True,
     )
     assert "pkga 1.0 has requirement pkgb==1.0" in result2.stderr, str(result2)
     assert "Successfully installed pkgB-2.0" in result2.stdout, str(result2)

tests/lib/__init__.py

@@ -423,9 +423,9 @@ class PipTestEnvironment(TestFileEnvironment):
         :param allow_stderr_error: whether a logged error is allowed in
             stderr.  Passing True for this argument implies
             `allow_stderr_warning` since warnings are weaker than errors.
-        :param expect_stderr: allow any stderr (equivalent to passing
-            `allow_stderr_error`).  This argument is an abbreviated version
-            of `allow_stderr_error` and is also kept for backwards
+        :param expect_stderr: whether to allow warnings in stderr (equivalent
+            to `allow_stderr_warning`).  This argument is an abbreviated
+            version of `allow_stderr_warning` and is also kept for backwards
             compatibility.
         """
         if self.verbose:
@@ -443,9 +443,12 @@ class PipTestEnvironment(TestFileEnvironment):
         allow_stderr_error = kw.pop('allow_stderr_error', None)
         allow_stderr_warning = kw.pop('allow_stderr_warning', None)
 
-        if kw.get('expect_error') or kw.get('expect_stderr'):
+        if kw.get('expect_error'):
             # Then default to allowing logged errors.
             allow_stderr_error = True
+        elif kw.get('expect_stderr'):
+            # Then default to allowing logged warnings.
+            allow_stderr_warning = True
 
         # Pass expect_stderr=True to allow any stderr.  We do this because
         # we do our checking of stderr further on in check_stderr().

tests/lib/test_lib.py

@@ -140,7 +140,6 @@ class TestPipTestEnvironment:
             self.run_stderr_with_prefix(script, prefix)
 
     @pytest.mark.parametrize('arg_name', (
-        'expect_stderr',
         'expect_error',
         'allow_stderr_error',
     ))