Function execTest

packages/babel-core/test/api.js:420–462

(passPerPreset)

    let aliasBaseType = null;

    function execTest(passPerPreset) {
      return transformSync("type Foo = number; let x = (y): Foo => y;", {
        sourceType: "script",
        passPerPreset: passPerPreset,
        presets: [
          // First preset with our plugin, "before"
          function () {
            return {
              plugins: [
                () => ({
                  visitor: {
                    Function: function (path) {
                      const alias = path.scope
                        .getProgramParent()
                        .path.get("body")[0].node;
                      if (!babel.types.isTypeAlias(alias)) return;

                      // In case of `passPerPreset` being `false`, the
                      // alias node is already removed by Flow plugin.
                      if (!alias) {
                        return;
                      }

                      // In case of `passPerPreset` being `true`, the
                      // alias node should still exist.
                      aliasBaseType = alias.right.type; // NumberTypeAnnotation
                    },
                  },
                }),
              ],
            };
          },

          // env preset
          [presetEnv, { targets: { browsers: "ie 6" } }],

          // Third preset for Flow.
          () => ({
            plugins: [pluginSyntaxFlow, pluginFlowStripTypes],
          }),
        ],
      });
    }

    // 1. passPerPreset: true