Revised both function and test for getExperimentBranch.

controllers/utils.js

@@ -33,10 +33,11 @@ function hasUserSignedUpForRelay(user) {
   return false;
 }
 
-function getExperimentBranch(req, language, sorterNum) {
+function getExperimentBranch(req, sorterNum = false, language = false) {
 
-  if (!sorterNum) {
+  if (sorterNum === false) {
     sorterNum = Math.floor(Math.random() * 100);
+    log.debug("No coinflip number provided. Coinflip number is ", sorterNum);
   }
 
   if (req.session.excludeFromExperiment && !req.query.experimentBranch) {
@@ -46,18 +47,20 @@ function getExperimentBranch(req, language, sorterNum) {
 
   // If we cannot parse req.headers["accept-language"], we should not
   // enroll users in the experiment.
-  if (!language || !req.headers || !req.headers["accept-language"]){
+  if (language && !req.headers || language && !req.headers["accept-language"]){
     log.debug("No headers or accept-language information present.");
     return false;
   }
 
-  // If the user doesn't have an English variant langauge selected as their primary language,
+  // If the user doesn't have the requested variant langauge selected as their primary language,
   // we do not enroll them in the experiment.
+  if (language) {
     const lang = req.headers["accept-language"].split(",");
     if (language && !lang[0].includes(language)) {
-    log.debug("Preferred language is not English variant: ", lang[0]);
+      log.debug(`Preferred language is not ${language} variant: ${lang[0]}`);
       return false;
     }
+  }
 
   // If URL param has experimentBranch entry, use that branch;
   if (req.query.experimentBranch) {

tests/controllers/home.test.js

@@ -2,10 +2,24 @@
 
 const AppConstants = require("../../app-constants");
 const home = require("../../controllers/home");
+const { getExperimentBranch } = require("../../controllers/utils");
 const { scanResult } = require("../../scan-results");
 
 let mockRequest = { fluentFormat: jest.fn(), csrfToken: jest.fn() };
 
+function mockRequestSessionReset(mockRequest) {
+  mockRequest.session = {
+    excludeFromExperiment: false,
+    experimentBranch: false,
+  };
+
+  mockRequest.headers = {
+    "accept-language": "en",
+  };
+
+  return mockRequest;
+}
+
 function addBreachesToMockRequest(mockRequest) {
   const mockBreaches = [
     {Name: "Test"},
@@ -60,3 +74,61 @@ test("notFound set status 404 and renders 404", () => {
   expect(mockStatusCallArgs[0]).toBe(404);
   expect(mockRenderCallArgs[0]).toBe("subpage");
 });
+
+test("Experiment 3 Cohort Assignment Unit Test", () => {
+
+  // Resets session and language after each test
+  mockRequestSessionReset(mockRequest);
+
+  // Set accept-language headers to German for first test.
+  mockRequest.headers = {
+    "accept-language": "de",
+  };
+
+// The session is excluded from the experiment because the set language is German.
+  let experimentBranch = getExperimentBranch(mockRequest, false, "en");
+  expect(experimentBranch).toBeFalsy();
+
+  mockRequestSessionReset(mockRequest);
+
+  // The session is assigned to the control group when the coin flip is 0;
+  let experimentNumber = 0;
+
+  experimentBranch = getExperimentBranch(mockRequest, experimentNumber);
+  expect(experimentBranch).toBe("va");
+
+  mockRequestSessionReset(mockRequest);
+
+  // The session is assigned to the control group when the coin flip is 29;
+  experimentNumber = 29;
+  experimentBranch = getExperimentBranch(mockRequest, experimentNumber);
+  expect(experimentBranch).toBe("va");
+
+  mockRequestSessionReset(mockRequest);
+
+  // The session is assigned to the treatment group when the coin flip is 30;
+  experimentNumber = 30;
+  experimentBranch = getExperimentBranch(mockRequest, experimentNumber);
+  expect(experimentBranch).toBe("vb");
+
+  mockRequestSessionReset(mockRequest);
+
+  // The session is assigned to the treatment group when the coin flip is 59;
+  experimentNumber = 59;
+  experimentBranch = getExperimentBranch(mockRequest, experimentNumber);
+  expect(experimentBranch).toBe("vb");
+
+  mockRequestSessionReset(mockRequest);
+
+  // The session is assigned to the treatment group when the coin flip is 60
+  experimentNumber = 60;
+  experimentBranch = getExperimentBranch(mockRequest, experimentNumber);
+  expect(experimentBranch).toBeFalsy();
+
+  mockRequestSessionReset(mockRequest);
+
+  // The session is excluded from the experiment when the coin flip is 99
+  experimentNumber = 99;
+  experimentBranch = getExperimentBranch(mockRequest, experimentNumber);
+  expect(experimentBranch).toBeFalsy();
+});