code: public void toContain(final Object item) {
          expectNotNull(this.getValue(), "Expected null to contain '%s'", item);
          expectTrue(this.getValue().contains(item), "Expected '%s' to contain '%s'", this.getValue(), item);
      }
docs: Checks if the stored {@code Collection} contains the provided item.
  <p>This method throws an {@code AssertionError} if
  <ul>
  <li>the stored {@code Collection} does not contain the passed {@code item}</li>
  <li>the given {@code Collection} is {@code null}</li>
  </ul>
  @param item the {@code Object} which the {@code Collection} should contain.