// Add failure test case.
	testCases = append(testCases, struct {
		partNum       int
		expectedIndex int
	}{6, -1})

	// Test them.
	for _, testCase := range testCases {
		if index := objectPartIndex(fi.Parts, testCase.partNum); index != testCase.expectedIndex {
			t.Fatalf("%+v: expected = %d, got: %d", testCase, testCase.expectedIndex, index)
		}
	}
}

// Test FileInfo.ObjectToPartOffset().

        void testFileIndex() throws CIFSException {
            // Given
            long expectedIndex = 12345L;
            when(mockResource.fileIndex()).thenReturn(expectedIndex);

            // When
            long index = mockResource.fileIndex();

            // Then
            assertEquals(expectedIndex, index, "Should return correct file index");