@Test
  public void testToJibContainerBuilder_classpathEmpty()
      throws IOException, InvalidImageReferenceException {
    try {
      JavaContainerBuilder.from("scratch").setMainClass("Hello").toContainerBuilder();
      Assert.fail();

    } catch (IllegalStateException ex) {
      Assert.assertEquals(
          "Failed to construct entrypoint because no files were added to the JavaContainerBuilder",
          ex.getMessage());
    }
  }
Gets the extraction paths in the specified layer of a give {@link BuildContext}.
jib-core/src/test/java/com/google/cloud/tools/jib/api/JavaContainerBuilderTest.java