code: public static <T extends Throwable> org.hamcrest.Matcher<T> hasMessage(String expectedMessage) {
          return new ThrowableMessageMatcher<>(expectedMessage);
      }
docs: EXAMPLE:
  <code>assertThat(caughtThrowable(), hasMessage("Index: 9, Size: 9"));</code>
  
  @param <T>
  the throwable subclass
  @param expectedMessage
  the expected throwable message
  @return Returns a matcher that matches an throwable if it has the given message.