test: migrate ModifiersTest to JUnit 5

[MartinWitt]

#3919

Change Log

The following bad smells are refactored:

JUnit4-@test

The JUnit 4 @Test annotation should be replaced with JUnit 5 @Test annotation.

JUnit4Assertion

The JUnit4 assertion should be replaced with JUnit5 Assertions.

The following has changed in the code:

JUnit4-@test

• Replaced junit 4 test annotation with junit 5 test annotation in testMethodWithVarargsDoesNotBecomeTransient
• Replaced junit 4 test annotation with junit 5 test annotation in testCtModifiableAddRemoveReturnCtModifiable
• Replaced junit 4 test annotation with junit 5 test annotation in testSetVisibility
• Replaced junit 4 test annotation with junit 5 test annotation in testGetModifiersHelpers
• Replaced junit 4 test annotation with junit 5 test annotation in testClearModifiersByEmptySet
• Replaced junit 4 test annotation with junit 5 test annotation in testClearModifiersByNull

JUnit4Assertion

• Transformed junit4 assert to junit 5 assertion in testMethodWithVarargsDoesNotBecomeTransient
• Transformed junit4 assert to junit 5 assertion in testCtModifiableAddRemoveReturnCtModifiable
• Transformed junit4 assert to junit 5 assertion in testSetVisibility
• Transformed junit4 assert to junit 5 assertion in testGetModifiersHelpers
• Transformed junit4 assert to junit 5 assertion in checkCtModifiableHelpersAssertion
• Transformed junit4 assert to junit 5 assertion in testClearModifiersByEmptySet
• Transformed junit4 assert to junit 5 assertion in testClearModifiersByNull