code: public void assertContains(@Nullable Description description, @Nullable String actual, @Nonnull String sequence) {
      checkNotNull(sequence);
      assertNotNull(description, actual);
      if (!actual.contains(sequence)) {
        String format = "expecting:<%s> to contain:<%s>";
        throw failures.failure(description, new BasicErrorMessageFactory(format, actual, sequence));
      }
    }
docs: Verifies that the <em>actual</em> {@code String} contains the given sequence.
  
  @param description the description of the <em>actual</em> {@code String}.
  @param actual the <em>actual</em> {@code String}.
  @param sequence the sequence to look for.
  @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 contain the given sequence.