@Override
  public MutableTreeRootHolder setRoots(Component root, Component reportRoot) {
    checkState(this.root == null, "root can not be set twice in holder");
    this.root = requireNonNull(root, "root can not be null");
    this.extendedTreeRoot = requireNonNull(reportRoot, "extended tree root can not be null");
    return this;
  }
@Test
  public void setRoot_throws_ISE_when_called_twice() {
    underTest.setRoots(DUMB_PROJECT, DUMB_PROJECT);

    assertThatThrownBy(() -> underTest.setRoots(null, DUMB_PROJECT))
      .isInstanceOf(IllegalStateException.class)
      .hasMessage("root can not be set twice in holder");
  }