Add GLEX frontend experiment helpers/spec helpers

app/assets/javascripts/experimentation/constants.js

 export const TRACKING_CONTEXT_SCHEMA = 'iglu:com.gitlab/gitlab_experiment/jsonschema/1-0-0';
 export const DEFAULT_VARIANT = 'control';
+export const CANDIDATE_VARIANT = 'candidate';

app/assets/javascripts/experimentation/utils.js

 // This file only applies to use of experiments through https://gitlab.com/gitlab-org/gitlab-experiment
 import { get } from 'lodash';
-import { DEFAULT_VARIANT } from './constants';
+import { DEFAULT_VARIANT, CANDIDATE_VARIANT } from './constants';
 
 export function getExperimentData(experimentName) {
   return get(window, ['gon', 'experiment', experimentName]);
@@ -13,3 +13,16 @@ export function isExperimentVariant(experimentName, variantName) {
 export function getExperimentVariant(experimentName) {
   return getExperimentData(experimentName)?.variant || DEFAULT_VARIANT;
 }
+
+export function experiment(experimentName, variants) {
+  const variant = getExperimentVariant(experimentName);
+
+  switch (variant) {
+    case DEFAULT_VARIANT:
+      return variants.use.call();
+    case CANDIDATE_VARIANT:
+      return variants.try.call();
+    default:
+      return variants[variant].call();
+  }
+}

spec/frontend/__helpers__/experimentation_helper.js

@@ -12,3 +12,16 @@ export function withGonExperiment(experimentKey, value = true) {
     window.gon = origGon;
   });
 }
+// This helper is for specs that use `gitlab-experiment` utilities, which have a different schema that gets pushed via Gon compared to `Experimentation Module`
+export function assignGitlabExperiment(experimentKey, variant) {
+  let origGon;
+
+  beforeEach(() => {
+    origGon = window.gon;
+    window.gon = { experiment: { [experimentKey]: { variant } } };
+  });
+
+  afterEach(() => {
+    window.gon = origGon;
+  });
+}

spec/frontend/experimentation/utils_spec.js

-import { DEFAULT_VARIANT } from '~/experimentation/constants';
+import { assignGitlabExperiment } from 'helpers/experimentation_helper';
+import { DEFAULT_VARIANT, CANDIDATE_VARIANT } from '~/experimentation/constants';
 import * as experimentUtils from '~/experimentation/utils';
 
-const TEST_KEY = 'abc';
-
 describe('experiment Utilities', () => {
-  const oldGon = window.gon;
-
-  afterEach(() => {
-    window.gon = oldGon;
-  });
+  const TEST_KEY = 'abc';
 
   describe('getExperimentData', () => {
-    it.each`
-      gon                                         | input         | output
-      ${{ experiment: { [TEST_KEY]: '_data_' } }} | ${[TEST_KEY]} | ${'_data_'}
-      ${{}}                                       | ${[TEST_KEY]} | ${undefined}
-    `('with input=$input and gon=$gon, returns $output', ({ gon, input, output }) => {
-      window.gon = gon;
+    describe.each`
+      gon                     | input         | output
+      ${[TEST_KEY, '_data_']} | ${[TEST_KEY]} | ${{ variant: '_data_' }}
+      ${[]}                   | ${[TEST_KEY]} | ${undefined}
+    `('with input=$input and gon=$gon', ({ gon, input, output }) => {
+      assignGitlabExperiment(...gon);
 
-      expect(experimentUtils.getExperimentData(...input)).toEqual(output);
+      it(`returns ${output}`, () => {
+        expect(experimentUtils.getExperimentData(...input)).toEqual(output);
+      });
     });
   });
 
   describe('isExperimentVariant', () => {
-    it.each`
-      gon                                                             | input                            | output
-      ${{ experiment: { [TEST_KEY]: { variant: 'control' } } }}       | ${[TEST_KEY, 'control']}         | ${true}
-      ${{ experiment: { [TEST_KEY]: { variant: '_variant_name' } } }} | ${[TEST_KEY, '_variant_name']}   | ${true}
-      ${{ experiment: { [TEST_KEY]: { variant: '_variant_name' } } }} | ${[TEST_KEY, '_bogus_name']}     | ${false}
-      ${{ experiment: { [TEST_KEY]: { variant: '_variant_name' } } }} | ${['boguskey', '_variant_name']} | ${false}
-      ${{}}                                                           | ${[TEST_KEY, '_variant_name']}   | ${false}
-    `('with input=$input and gon=$gon, returns $output', ({ gon, input, output }) => {
-      window.gon = gon;
+    describe.each`
+      gon                            | input                            | output
+      ${[TEST_KEY, DEFAULT_VARIANT]} | ${[TEST_KEY, DEFAULT_VARIANT]}   | ${true}
+      ${[TEST_KEY, '_variant_name']} | ${[TEST_KEY, '_variant_name']}   | ${true}
+      ${[TEST_KEY, '_variant_name']} | ${[TEST_KEY, '_bogus_name']}     | ${false}
+      ${[TEST_KEY, '_variant_name']} | ${['boguskey', '_variant_name']} | ${false}
+      ${[]}                          | ${[TEST_KEY, '_variant_name']}   | ${false}
+    `('with input=$input and gon=$gon', ({ gon, input, output }) => {
+      assignGitlabExperiment(...gon);
+
+      it(`returns ${output}`, () => {
+        expect(experimentUtils.isExperimentVariant(...input)).toEqual(output);
+      });
+    });
+  });
+
+  describe('experiment', () => {
+    const controlSpy = jest.fn();
+    const candidateSpy = jest.fn();
+    const getUpStandUpSpy = jest.fn();
+
+    const variants = {
+      use: controlSpy,
+      try: candidateSpy,
+      get_up_stand_up: getUpStandUpSpy,
+    };
+
+    describe('when there is no experiment data', () => {
+      it('calls control variant', () => {
+        experimentUtils.experiment('marley', variants);
+        expect(controlSpy).toHaveBeenCalled();
+      });
+    });
+
+    describe('when experiment variant is "control"', () => {
+      assignGitlabExperiment('marley', DEFAULT_VARIANT);
+
+      it('calls the control variant', () => {
+        experimentUtils.experiment('marley', variants);
+        expect(controlSpy).toHaveBeenCalled();
+      });
+    });
+
+    describe('when experiment variant is "candidate"', () => {
+      assignGitlabExperiment('marley', CANDIDATE_VARIANT);
+
+      it('calls the candidate variant', () => {
+        experimentUtils.experiment('marley', variants);
+        expect(candidateSpy).toHaveBeenCalled();
+      });
+    });
+
+    describe('when experiment variant is "get_up_stand_up"', () => {
+      assignGitlabExperiment('marley', 'get_up_stand_up');
 
-      expect(experimentUtils.isExperimentVariant(...input)).toEqual(output);
+      it('calls the get-up-stand-up variant', () => {
+        experimentUtils.experiment('marley', variants);
+        expect(getUpStandUpSpy).toHaveBeenCalled();
+      });
     });
   });
 
   describe('getExperimentVariant', () => {
     it.each`
-      gon                                                         | input         | output
-      ${{ experiment: { [TEST_KEY]: { variant: 'control' } } }}   | ${[TEST_KEY]} | ${'control'}
-      ${{ experiment: { [TEST_KEY]: { variant: 'candidate' } } }} | ${[TEST_KEY]} | ${'candidate'}
-      ${{}}                                                       | ${[TEST_KEY]} | ${DEFAULT_VARIANT}
+      gon                                                               | input         | output
+      ${{ experiment: { [TEST_KEY]: { variant: DEFAULT_VARIANT } } }}   | ${[TEST_KEY]} | ${DEFAULT_VARIANT}
+      ${{ experiment: { [TEST_KEY]: { variant: CANDIDATE_VARIANT } } }} | ${[TEST_KEY]} | ${CANDIDATE_VARIANT}
+      ${{}}                                                             | ${[TEST_KEY]} | ${DEFAULT_VARIANT}
     `('with input=$input and gon=$gon, returns $output', ({ gon, input, output }) => {
       window.gon = gon;