code: public void assertGreaterThan(Description description, Character actual, char other) {
      assertNotNull(description, actual);
      if (!isGreaterThan(actual, other)) {
        throw failures.failure(description, shouldBeGreaterThan(actual, other));
      }
    }
docs: Asserts that the actual value is greater than the other one.
  
  @param description contains information about the assertion.
  @param actual the actual value.
  @param other the value to compare the actual value to.
  @throws AssertionError if the actual value is {@code null}.
  @throws AssertionError if the actual value is not greater than the other one: this assertion will fail if the
  actual value is equal to or less than the other value.