add test

tests/functional/test_install.py

@@ -2351,3 +2351,48 @@ def test_install_8559_wheel_package_present(
         allow_stderr_warning=False,
     )
     assert DEPRECATION_MSG_PREFIX not in result.stderr
+
+
+@pytest.mark.skipif(
+    sys.version_info < (3, 11),
+    reason="3.11 required to find distributions via importlib metadata"
+)
+def test_install_existing_memory_distribution(script: PipTestEnvironment):
+    sitecustomize_text = textwrap.dedent(
+        """
+        import sys
+        from importlib.metadata import Distribution, DistributionFinder
+        
+        
+        EXAMPLE_METADATA = '''Metadata-Version: 2.1
+        Name: example
+        Version: 1.0.0
+        
+        '''
+
+        class ExampleDistribution(Distribution):
+            def locate_file(self, path):
+                return path
+        
+            def read_text(self, filename):
+                if filename == 'METADATA':
+                    return EXAMPLE_METADATA
+        
+        
+        class CustomFinder(DistributionFinder):
+            def find_distributions(self, context=None):
+                return [ExampleDistribution()]
+        
+        
+        sys.meta_path.append(CustomFinder())
+        """
+    )
+    with open(script.site_packages_path / 'sitecustomize.py', 'w') as sitecustomize_file:
+        sitecustomize_file.write(sitecustomize_text)
+
+    result = script.pip(
+        "install",
+        "example"
+    )
+
+    assert "Requirement already satisfied: example in <memory>" in result.stdout