Shuffle test runners

Author: scraggo

docs/test-runner.md

@@ -22,6 +22,8 @@ This application is a test-runner that can:
 
 The number and length of the authored tests simulate a "true" test run in a significantly sized enterprise codebase. Each test runner has a template that will run the _same exact_ test blocks and take the _same exact_ amount of time in each block. (This is done with a `setTimeout` with a time that increases with each iteration of the loop that generates the test block.)
 
+To account for a bias in ordering, the scripts corresponding to each test runner are shuffled. This ensures that the suites for each test runner are never called in the same sequence.
+
 ## Running the tests
 
 `npm install` to install all the packages.

src/index.js

@@ -1,7 +1,9 @@
 const { fullCircle } = require('./fullCircle');
 const { range } = require('./range');
+const { shuffle } = require('./shuffle');
 
 module.exports = {
   fullCircle,
   range,
+  shuffle,
 };

src/runAllTests.js

@@ -1,8 +1,10 @@
 const execa = require('execa');
+const { shuffle } = require('./');
 
 // CONSTANTS
 
-const testRunners = ['ava', 'jest', 'mocha', 'parallel'];
+const TEST_RUNNERS = ['ava', 'jest', 'mocha', 'parallel'];
+const testRunners = shuffle(TEST_RUNNERS);
 
 // UTILS
 
@@ -104,8 +106,8 @@ const main = () => {
 
     console.log(`-*-*-*-*-*-*-*-*-*-*-
       RESULTS
--*-*-*-*-*-*-*-*-*-*-`);
-
+-*-*-*-*-*-*-*-*-*-*-\n`);
+    console.log('order:', testRunners, '\n');
     logResults(testResults);
   } catch (error) {
     console.error(error);

src/shuffle.js

@@ -0,0 +1,19 @@
+/**
+ * Fisher Yates Shuffle
+ * @param {Array} arrInput
+ * @param {Object} [options={}]
+ * @param {boolean} [options.clone=false]
+ * @returns {Array} shuffled array
+ */
+function shuffle(arrInput, { clone = false } = {}) {
+  const arr = clone ? arrInput.slice() : arrInput;
+
+  for (let i = arr.length - 1; i > 0; i -= 1) {
+    const j = Math.floor(Math.random() * (i + 1));
+    [arr[i], arr[j]] = [arr[j], arr[i]];
+  }
+
+  return arr;
+}
+
+module.exports = { shuffle };

test/src/range.spec.js

@@ -1,5 +1,3 @@
-// const { expect } = require('chai');
-
 const { range } = require('../../src');
 
 describe('range', function() {
@@ -17,9 +15,9 @@ describe('range', function() {
     expect(res).to.deep.equal([]);
   });
   it('throws error under bad conditions', function() {
-    expect(() => range()).to.throw;
-    expect(() => range(-1)).to.throw;
-    expect(() => range(-2, -1)).to.throw;
-    expect(() => range(2, 1)).to.throw;
+    expect(() => range()).to.throw();
+    expect(() => range(-1)).to.throw();
+    expect(() => range(-2, -1)).to.throw();
+    expect(() => range(2, 1)).to.throw();
   });
 });

test/src/shuffle.spec.js

@@ -0,0 +1,17 @@
+const { range, shuffle } = require('../../src');
+
+describe('shuffle', function() {
+  it('returns array of same length', function() {
+    expect(shuffle([0, 1])).to.have.length(2);
+    expect(shuffle([0, 1, 2])).to.have.length(3);
+    expect(shuffle([0, 1, 2, 3])).to.have.length(4);
+  });
+
+  it('eventually shuffles cloned array', function() {
+    const arr = [0, 1];
+    const NUM_OF_RUNS = 5;
+    const runs = range(0, NUM_OF_RUNS).map(() => shuffle(arr, { clone: true }));
+
+    expect(runs).to.deep.include([1, 0]);
+  });
+});