treeForAddonTestSupport(tree) {
    if (!tree) {
      return tree;
    }

    let namespacedTree = new Funnel(tree, {
      srcDir: '/',
      destDir: `/${this.moduleName()}/test-support`,
      annotation: `Addon#treeForTestSupport (${this.name})`,
    });

    if (registryHasPreprocessor(this.registry, 'js')) {
      return this.preprocessJs(namespacedTree, '/', this.name, {
        registry: this.registry,
        treeType: 'addon-test-support',
      });
    }

    throw new SilentError(
      `Addon test-support files were detected in \`${this._treePathFor('addon-test-support')}\`, but no JavaScript ` +
        `preprocessor was found for \`${this.name}\`. Please make sure to add a preprocessor ` +
        `(most likely \`ember-cli-babel\`) to \`dependencies\` (NOT \`devDependencies\`) in ` +
        `\`${this.name}\`'s \`package.json\`.`
    );
  }
Returns the tree for all test files namespaced to a given addon.

   @public
   @method treeForAddonTestSupport
   @param {Tree} tree
   @return {Tree}