code: public void toHaveSize(final int size) {
          expectNotNull(this.getValue(), "Expected null to have size '%s'", size);
  		expectTrue(this.getValue().size() == size, "Expected '%s' to have a size of %d, instead has a size of %d", this.getValue(), size, this.getValue().size());
  	}
docs: Checks if the stored {@code Map} has a given {@code size}.
  <p>This method throws an {@code AssertionError} if
  <ul>
  <li>the stored {@code Map} does not have the given {@code size}</li>
  <li>the stored {@code Map} is {@code null}</li>
  </ul>
  @param size the expected size