@Override
  public void installed(CoreExtension coreExtension) {
    checkInitialized();
    requireNonNull(coreExtension, "coreExtension can't be null");
    checkArgument(coreExtensions.contains(coreExtension), "Specified CoreExtension has not been loaded first");

    this.installedCoreExtensions.add(coreExtension);
  }
@Test
  public void installed_fails_with_ISE_if_called_before_setLoadedCoreExtensions() {
    CoreExtension coreExtension = newCoreExtension();

    assertThatThrownBy(() -> underTest.installed(coreExtension))
      .isInstanceOf(IllegalStateException.class)
      .hasMessage("Repository has not been initialized yet");
  }