code: public void toBeInstanceOf(Class<?> expectedClass) {
  		expectTrue(expectedClass.isInstance(value), "Expected '%s' to be instance of '%s'", this.value, expectedClass.getName());
  	}
docs: Checks if the stored value is an instance of the {@code expectedClass}
  <p>This method throws an {@code AssertionError} if the stored value is not of instance of {@code expectedClass}.
  @param expectedClass The expected class