@Test
public void testMakeLogMessage_exceptionCodeResolver_is_null() {

    // do setup.
    Exception ex = new FileNotFoundException("occur file not found exception.");
    // do test.
    String actualLogMessage = testTarget.makeLogMessage(ex);
    // do assert.
    String expectedLogMessage = "[UNDEFINED-CODE] occur file not found exception.";
    assertThat(actualLogMessage, is(expectedLogMessage));
}