util/collect/collect.go (1)

51-62: New Filter function is well-implemented but needs better documentation

The implementation is efficient and correctly handles edge cases by:

• Pre-allocating output slice capacity to avoid unnecessary reallocations
• Properly handling nil/empty inputs
• Using generics to work with any slice type

However, the documentation is quite minimal compared to other functions in this package.

Consider expanding the documentation to include:

• How it handles nil/empty inputs
• That it returns a new slice rather than modifying the input
• An example of usage
• The relationship with the similar All function

-// Filter a slice using a filter func (T) => (bool).
+// Filter creates a new slice containing only the elements from input that satisfy filterFunc.
+// Empty or nil input returns nil output.
+// This is similar to All but pre-allocates the output slice for better performance.
func Filter[I ~[]T, T any](input I, filterFunc func(t T) bool) (output []T) {

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systemd/drop_ins_test.go (3)

44-57: Consider adding test cases for edge conditions.

While the test covers the basic success and failure cases, consider adding tests for edge conditions such as permission errors or when the path is a directory instead of a file to ensure robust error handling.

tests := []struct {
	name          string
	file          string
	setupFs       func() afero.Fs
	expectedValue bool
}{
	// existing test cases...
+	{
+		name: "path is a directory",
+		file: "/path/to/dir",
+		setupFs: func() afero.Fs {
+			testFs := afero.NewMemMapFs()
+			err := testFs.Mkdir("/path/to/dir", 0755)
+			require.NoError(t, err)
+			return testFs
+		},
+		expectedValue: false,
+	},
+	{
+		name: "permission error",
+		file: "/path/to/no-permission-file",
+		setupFs: func() afero.Fs {
+			// You'd need to use a filesystem implementation that can simulate permission errors
+			// This is a simplified example
+			testFs := afero.NewMemMapFs()
+			// Setup code that would result in permission error when accessing file
+			return testFs
+		},
+		expectedValue: false,
+	},
}

---

53-54: Verify that errors are logged appropriately.

According to the PR objectives, an error message should be displayed in the console when drop-in files are missing. Consider extending the test to verify that appropriate logging occurs when files don't exist.

You could capture log output and verify it contains the expected error message when a file doesn't exist:

result := unit.DropInFileExists(tc.file)
assert.Equal(t, tc.expectedValue, result)
+if !tc.expectedValue {
+   // Assuming there's a way to capture and verify logs in your application
+   // This is a conceptual example; implementation would depend on your logging framework
+   assert.Contains(t, capturedLogs, "Error accessing drop-in file")
+}

---

1-58: Consider adding integration test for the filtering behavior.

While this unit test covers the file existence check well, consider adding an integration test that verifies the filtering behavior in the context of systemd unit generation. This would ensure that missing files are properly excluded when generating configurations.

You could add a separate test function that:

1. Sets up a filesystem with both existing and non-existing drop-in files
2. Calls the relevant function that uses DropInFileExists for filtering
3. Verifies that only existing files are included in the resulting configuration

This would provide end-to-end validation of the fix described in the PR objectives.

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systemd/drop_ins_test.go (1)

13-68: Consider adding a test for permission errors

While the current tests cover basic existence checks, consider adding a test case for permission errors that might occur when checking file existence. This would ensure the method handles permission-related issues correctly.

{
    name: "permission error",
    file: "/path/to/protected",
    setupFs: func() afero.Fs {
        // Use a filesystem implementation that can simulate permission errors
        // or mock the filesystem operations to return a permission error
        testFs := &mockFs{} // Custom mock that returns permission error
        return testFs
    },
    expectedValue: false, // Or however the function should behave with permission errors
},

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