code: public void assertStartsWith(@Nullable Description description, @Nullable String actual, @Nonnull String prefix) {
      checkNotNull(prefix);
      assertNotNull(description, actual);
      if (!actual.startsWith(prefix)) {
        throw failures.failure(description, shouldStartWith(actual, prefix));
      }
    }
docs: Verifies that the <em>actual</em> {@code String} starts with the given prefix.
  
  @param description the description of the <em>actual</em> {@code String}.
  @param actual the <em>actual</em> {@code String}.
  @param prefix the given prefix.
  @throws NullPointerException if the given sequence is {@code null}.
  @throws AssertionError if the <em>actual</em> {@code String} is {@code null}.
  @throws AssertionError if the <em>actual</em> {@code String} does not start with the given prefix.