@Test public void testRomanSystemConvertion() { // Arrange numberConverter.setArabicToRomanConverter(mockedArabicToRomanConverter); // Stubbing when(mockedArabicToRomanConverter.convert(1)).thenReturn("I"); // Act String result = numberConverter.convert(1, "ROMAN"); // Assert verify(mockedArabicToRomanConverter).convert(1); assertEquals("I", result); }