### Question:
Assert { public static void isNull(Object obj) { isNull(obj, "Expected null reference, but was {0}", obj); }  static void isNull(Object obj); static void isNull(Object obj, String messagePattern, Object... args); static void notNull(Object obj); static void notNull(Object obj, String messagePattern, Object... args); static void isTrue(boolean bool, String messagePattern, Object... args); static void isFalse(boolean bool, String messagePattern, Object... args); static IllegalStateException shouldNeverHappen(Throwable th);  }### Answer:
@Test public void testIsNull_Ok() throws Exception { isNull(null); isNull(null, "msg"); }
@Test(expectedExceptions = IllegalArgumentException.class) public void testIsNull_Fail() throws Exception { isNull(DUMMY); }
@Test(expectedExceptions = IllegalArgumentException.class) public void testIsNull_Fail_withMsg() throws Exception { isNull(DUMMY, "msg"); }