Prevent new JS files in shared folder (#17737)

* Prevent new JS files in shared folder

* migrate to typescript

* fix types

* cleanup

.github/workflows/fitness-functions.yml

@@ -24,5 +24,5 @@ jobs:
         run: |
           # git fetch origin $HEAD_REF
           # git fetch origin $BASE_REF
-          # git diff origin/$BASE_REF origin/$HEAD_REF -- . ':(exclude)development/fitness-functions/*' > diff
+          # git diff origin/$BASE_REF origin/$HEAD_REF -- . > diff
           # npm run fitness-functions -- "ci" "./diff"

development/fitness-functions/check-mocha-syntax.js

@@ -1,44 +0,0 @@
-const {
-  EXCLUDE_E2E_TESTS_REGEX,
-  filterDiffAdditions,
-  filterDiffByFilePath,
-  hasNumberOfCodeBlocksIncreased,
-} = require('./shared');
-
-function checkMochaSyntax(diff) {
-  const ruleHeading = 'favor-jest-instead-of-mocha';
-  const codeBlocks = [
-    "import { strict as assert } from 'assert';",
-    'assert.deepEqual',
-    'assert.equal',
-    'assert.rejects',
-    'assert.strictEqual',
-    'sinon.',
-  ];
-
-  console.log(`\nChecking ${ruleHeading}...`);
-
-  const diffByFilePath = filterDiffByFilePath(diff, EXCLUDE_E2E_TESTS_REGEX);
-  const diffAdditions = filterDiffAdditions(diffByFilePath);
-  const hashmap = hasNumberOfCodeBlocksIncreased(diffAdditions, codeBlocks);
-
-  Object.keys(hashmap).forEach((key) => {
-    if (hashmap[key]) {
-      console.error(`Number of occurences of "${key}" have increased.`);
-    }
-  });
-
-  if (Object.values(hashmap).includes(true)) {
-    console.error(
-      `...changes have not been accepted by the fitness function.\nFor more info, see: https://github.com/MetaMask/metamask-extension/blob/develop/docs/testing.md#${ruleHeading}`,
-    );
-    process.exit(1);
-  } else {
-    console.log(
-      `...number of occurences has not increased for any code block.`,
-    );
-    process.exit(0);
-  }
-}
-
-module.exports = { checkMochaSyntax };

development/fitness-functions/common/constants.test.ts

@@ -0,0 +1,105 @@
+import { EXCLUDE_E2E_TESTS_REGEX, SHARED_FOLDER_JS_REGEX } from './constants';
+
+describe('Regular Expressions used in Fitness Functions', (): void => {
+  describe(`EXCLUDE_E2E_TESTS_REGEX "${EXCLUDE_E2E_TESTS_REGEX}"`, (): void => {
+    const PATHS_IT_SHOULD_MATCH = [
+      'file.js',
+      'path/file.js',
+      'much/longer/path/file.js',
+      'file.ts',
+      'path/file.ts',
+      'much/longer/path/file.ts',
+      'file.jsx',
+      'path/file.jsx',
+      'much/longer/path/file.jsx',
+    ];
+
+    const PATHS_IT_SHOULD_NOT_MATCH = [
+      // any without JS, TS, JSX or TSX extension
+      'file',
+      'file.extension',
+      'path/file.extension',
+      'much/longer/path/file.extension',
+      // any in the test/e2e directory
+      'test/e2e/file',
+      'test/e2e/file.extension',
+      'test/e2e/path/file.extension',
+      'test/e2e/much/longer/path/file.extension',
+      'test/e2e/file.js',
+      'test/e2e/path/file.ts',
+      'test/e2e/much/longer/path/file.jsx',
+      'test/e2e/much/longer/path/file.tsx',
+      // any in the development/fitness-functions directory
+      'development/fitness-functions/file',
+      'development/fitness-functions/file.extension',
+      'development/fitness-functions/path/file.extension',
+      'development/fitness-functions/much/longer/path/file.extension',
+      'development/fitness-functions/file.js',
+      'development/fitness-functions/path/file.ts',
+      'development/fitness-functions/much/longer/path/file.jsx',
+      'development/fitness-functions/much/longer/path/file.tsx',
+    ];
+
+    describe('included paths', (): void => {
+      PATHS_IT_SHOULD_MATCH.forEach((path: string): void => {
+        it(`should match "${path}"`, (): void => {
+          const result = new RegExp(EXCLUDE_E2E_TESTS_REGEX, 'u').test(path);
+
+          expect(result).toStrictEqual(true);
+        });
+      });
+    });
+
+    describe('excluded paths', (): void => {
+      PATHS_IT_SHOULD_NOT_MATCH.forEach((path: string): void => {
+        it(`should not match "${path}"`, (): void => {
+          const result = new RegExp(EXCLUDE_E2E_TESTS_REGEX, 'u').test(path);
+
+          expect(result).toStrictEqual(false);
+        });
+      });
+    });
+  });
+
+  describe(`SHARED_FOLDER_JS_REGEX "${SHARED_FOLDER_JS_REGEX}"`, (): void => {
+    const PATHS_IT_SHOULD_MATCH = [
+      'shared/file.js',
+      'shared/path/file.js',
+      'shared/much/longer/path/file.js',
+      'shared/file.jsx',
+      'shared/path/file.jsx',
+      'shared/much/longer/path/file.jsx',
+    ];
+
+    const PATHS_IT_SHOULD_NOT_MATCH = [
+      // any without JS or JSX extension
+      'file',
+      'file.extension',
+      'path/file.extension',
+      'much/longer/path/file.extension',
+      'file.ts',
+      'path/file.ts',
+      'much/longer/path/file.tsx',
+    ];
+
+    describe('included paths', (): void => {
+      PATHS_IT_SHOULD_MATCH.forEach((path: string): void => {
+        it(`should match "${path}"`, (): void => {
+          const result = new RegExp(SHARED_FOLDER_JS_REGEX, 'u').test(path);
+
+          expect(result).toStrictEqual(true);
+        });
+      });
+    });
+
+    describe('excluded paths', (): void => {
+      PATHS_IT_SHOULD_NOT_MATCH.forEach((path: string): void => {
+        it(`should not match "${path}"`, (): void => {
+          const result = new RegExp(SHARED_FOLDER_JS_REGEX, 'u').test(path);
+
+          expect(result).toStrictEqual(false);
+        });
+      });
+    });
+  });
+});

development/fitness-functions/common/constants.ts

@@ -0,0 +1,15 @@
+// include JS, TS, JSX, TSX files only excluding files in the e2e tests and
+// fitness functions directories
+const EXCLUDE_E2E_TESTS_REGEX =
+  '^(?!test/e2e)(?!development/fitness).*.(js|ts|jsx|tsx)$';
+
+// include JS and JSX files in the shared directory only
+const SHARED_FOLDER_JS_REGEX = '^(shared).*.(js|jsx)$';
+
+enum AUTOMATION_TYPE {
+  CI = 'ci',
+  PRE_COMMIT_HOOK = 'pre-commit-hook',
+  PRE_PUSH_HOOK = 'pre-push-hook',
+}
+
+export { EXCLUDE_E2E_TESTS_REGEX, SHARED_FOLDER_JS_REGEX, AUTOMATION_TYPE };

development/fitness-functions/common/get-diff.ts

@@ -0,0 +1,54 @@
+import { execSync } from 'child_process';
+import fs from 'fs';
+import { AUTOMATION_TYPE } from './constants';
+
+function getDiffByAutomationType(
+  automationType: AUTOMATION_TYPE,
+): string | undefined {
+  if (!Object.values(AUTOMATION_TYPE).includes(automationType)) {
+    console.error('Invalid automation type.');
+    process.exit(1);
+  }
+
+  let diff;
+  if (automationType === AUTOMATION_TYPE.CI) {
+    const optionalArguments = process.argv.slice(3);
+    if (optionalArguments.length !== 1) {
+      console.error('Invalid number of arguments.');
+      process.exit(1);
+    }
+
+    diff = getCIDiff(optionalArguments[0]);
+  } else if (automationType === AUTOMATION_TYPE.PRE_COMMIT_HOOK) {
+    diff = getPreCommitHookDiff();
+  } else if (automationType === AUTOMATION_TYPE.PRE_PUSH_HOOK) {
+    diff = getPrePushHookDiff();
+  }
+
+  return diff;
+}
+
+function getCIDiff(path: string): string {
+  return fs.readFileSync(path, {
+    encoding: 'utf8',
+    flag: 'r',
+  });
+}
+
+function getPreCommitHookDiff(): string {
+  return execSync(`git diff --cached HEAD`).toString().trim();
+}
+
+function getPrePushHookDiff(): string {
+  const currentBranch = execSync(`git rev-parse --abbrev-ref HEAD`)
+    .toString()
+    .trim();
+
+  return execSync(
+    `git diff ${currentBranch} origin/${currentBranch} -- . ':(exclude)development/fitness-functions/'`,
+  )
+    .toString()
+    .trim();
+}
+
+export { getDiffByAutomationType };

development/fitness-functions/common/shared.test.ts

@@ -1,46 +1,48 @@
-const {
-  EXCLUDE_E2E_TESTS_REGEX,
-  filterDiffAdditions,
+import {
+  filterDiffLineAdditions,
   hasNumberOfCodeBlocksIncreased,
   filterDiffByFilePath,
-} = require('./shared');
+  filterDiffFileCreations,
+} from './shared';
+import { generateCreateFileDiff, generateModifyFilesDiff } from './test-data';
 
-const generateCreateFileDiff = (filePath, content) => `
-diff --git a/${filePath} b/${filePath}
-new file mode 100644
-index 000000000..30d74d258
---- /dev/null
-+++ b/${filePath}
-@@ -0,0 +1 @@
-+${content}
-`;
-
-const generateModifyFilesDiff = (filePath, addition, removal) => `
-diff --git a/${filePath} b/${filePath}
-index 57d5de75c..808d8ba37 100644
---- a/${filePath}
-+++ b/${filePath}
-@@ -1,3 +1,8 @@
-+${addition}
-@@ -34,33 +39,4 @@
--${removal}
-`;
-
-describe('filterDiffAdditions()', () => {
-  it('should return code additions in the diff', () => {
+describe('filterDiffLineAdditions()', (): void => {
+  it('should return code additions in the diff', (): void => {
     const testFilePath = 'new-file.js';
     const testAddition = 'foo';
     const testFileDiff = generateCreateFileDiff(testFilePath, testAddition);
 
-    const actualResult = filterDiffAdditions(testFileDiff);
+    const actualResult = filterDiffLineAdditions(testFileDiff);
     const expectedResult = `+${testAddition}`;
 
     expect(actualResult).toStrictEqual(expectedResult);
   });
 });
 
-describe('hasNumberOfCodeBlocksIncreased()', () => {
-  it('should show which code blocks have increased', () => {
+describe('filterDiffFileCreations()', (): void => {
+  it('should return code additions in the diff', (): void => {
+    const testFileDiff = [
+      generateModifyFilesDiff('new-file.ts', 'foo', 'bar'),
+      generateCreateFileDiff('old-file.js', 'ping'),
+      generateModifyFilesDiff('old-file.jsx', 'yin', 'yang'),
+    ].join('');
+
+    const actualResult = filterDiffFileCreations(testFileDiff);
+
+    expect(actualResult).toMatchInlineSnapshot(`
+      "diff --git a/old-file.js b/old-file.js
+      new file mode 100644
+      index 000000000..30d74d258
+      --- /dev/null
+      +++ b/old-file.js
+      @@ -0,0 +1 @@
+      +ping"
+    `);
+  });
+});
+
+describe('hasNumberOfCodeBlocksIncreased()', (): void => {
+  it('should show which code blocks have increased', (): void => {
     const testDiffFragment = `
     +foo
     +bar
@@ -57,14 +59,14 @@ describe('hasNumberOfCodeBlocksIncreased()', () => {
   });
 });
 
-describe('filterDiffByFilePath()', () => {
+describe('filterDiffByFilePath()', (): void => {
   const testFileDiff = [
     generateModifyFilesDiff('new-file.ts', 'foo', 'bar'),
     generateModifyFilesDiff('old-file.js', 'ping', 'pong'),
     generateModifyFilesDiff('old-file.jsx', 'yin', 'yang'),
   ].join('');
 
-  it('should return the right diff for a generic matcher', () => {
+  it('should return the right diff for a generic matcher', (): void => {
     const actualResult = filterDiffByFilePath(
       testFileDiff,
       '.*/.*.(js|ts)$|.*.(js|ts)$',
@@ -90,7 +92,7 @@ describe('filterDiffByFilePath()', () => {
     `);
   });
 
-  it('should return the right diff for a specific file in any dir matcher', () => {
+  it('should return the right diff for a specific file in any dir matcher', (): void => {
     const actualResult = filterDiffByFilePath(testFileDiff, '.*old-file.js$');
 
     expect(actualResult).toMatchInlineSnapshot(`
@@ -105,7 +107,7 @@ describe('filterDiffByFilePath()', () => {
     `);
   });
 
-  it('should return the right diff for a multiple file extension (OR) matcher', () => {
+  it('should return the right diff for a multiple file extension (OR) matcher', (): void => {
     const actualResult = filterDiffByFilePath(
       testFileDiff,
       '^(./)*old-file.(js|ts|jsx)$',
@@ -131,7 +133,7 @@ describe('filterDiffByFilePath()', () => {
     `);
   });
 
-  it('should return the right diff for a file name negation matcher', () => {
+  it('should return the right diff for a file name negation matcher', (): void => {
     const actualResult = filterDiffByFilePath(
       testFileDiff,
       '^(?!.*old-file.js$).*.[a-zA-Z]+$',
@@ -157,51 +159,3 @@ describe('filterDiffByFilePath()', () => {
     `);
   });
 });
-
-describe(`EXCLUDE_E2E_TESTS_REGEX "${EXCLUDE_E2E_TESTS_REGEX}"`, () => {
-  const PATHS_IT_SHOULD_MATCH = [
-    'file.js',
-    'path/file.js',
-    'much/longer/path/file.js',
-    'file.ts',
-    'path/file.ts',
-    'much/longer/path/file.ts',
-    'file.jsx',
-    'path/file.jsx',
-    'much/longer/path/file.jsx',
-  ];
-
-  const PATHS_IT_SHOULD_NOT_MATCH = [
-    'test/e2e/file',
-    'test/e2e/file.extension',
-    'test/e2e/path/file.extension',
-    'test/e2e/much/longer/path/file.extension',
-    'test/e2e/file.js',
-    'test/e2e/path/file.ts',
-    'test/e2e/much/longer/path/file.jsx',
-    'file',
-    'file.extension',
-    'path/file.extension',
-    'much/longer/path/file.extension',
-  ];
-
-  describe('included paths', () => {
-    PATHS_IT_SHOULD_MATCH.forEach((path) => {
-      it(`should match "${path}"`, () => {
-        const result = new RegExp(EXCLUDE_E2E_TESTS_REGEX, 'u').test(path);
-
-        expect(result).toStrictEqual(true);
-      });
-    });
-  });
-
-  describe('excluded paths', () => {
-    PATHS_IT_SHOULD_NOT_MATCH.forEach((path) => {
-      it(`should not match "${path}"`, () => {
-        const result = new RegExp(EXCLUDE_E2E_TESTS_REGEX, 'u').test(path);
-
-        expect(result).toStrictEqual(false);
-      });
-    });
-  });
-});

development/fitness-functions/common/shared.ts

@@ -1,6 +1,4 @@
-const EXCLUDE_E2E_TESTS_REGEX = '^(?!test/e2e/).*.(js|ts|jsx)$';
-
-function filterDiffByFilePath(diff, regex) {
+function filterDiffByFilePath(diff: string, regex: string): string {
   // split by `diff --git` and remove the first element which is empty
   const diffBlocks = diff.split(`diff --git`).slice(1);
 
@@ -34,7 +32,7 @@ function filterDiffByFilePath(diff, regex) {
   return filteredDiff;
 }
 
-function filterDiffAdditions(diff) {
+function filterDiffLineAdditions(diff: string): string {
   const diffLines = diff.split('\n');
 
   const diffAdditionLines = diffLines.filter((line) => {
@@ -46,10 +44,36 @@ function filterDiffAdditions(diff) {
   return diffAdditionLines.join('/n');
 }
 
-function hasNumberOfCodeBlocksIncreased(diffFragment, codeBlocks) {
+function filterDiffFileCreations(diff: string): string {
+  // split by `diff --git` and remove the first element which is empty
+  const diffBlocks = diff.split(`diff --git`).slice(1);
+
+  const filteredDiff = diffBlocks
+    .map((block) => block.trim())
+    .filter((block) => {
+      const isFileCreationLine =
+        block
+          // get the second line of the block which has the file mode
+          .split('\n')[1]
+          .trim()
+          .substring(0, 13) === 'new file mode';
+
+      return isFileCreationLine;
+    })
+    // prepend `git --diff` to each block
+    .map((block) => `diff --git ${block}`)
+    .join('\n');
+
+  return filteredDiff;
+}
+
+function hasNumberOfCodeBlocksIncreased(
+  diffFragment: string,
+  codeBlocks: string[],
+): { [codeBlock: string]: boolean } {
   const diffLines = diffFragment.split('\n');
 
-  const codeBlockFound = {};
+  const codeBlockFound: { [codeBlock: string]: boolean } = {};
 
   for (const codeBlock of codeBlocks) {
     codeBlockFound[codeBlock] = false;
@@ -65,9 +89,9 @@ function hasNumberOfCodeBlocksIncreased(diffFragment, codeBlocks) {
   return codeBlockFound;
 }
 
-module.exports = {
-  EXCLUDE_E2E_TESTS_REGEX,
+export {
   filterDiffByFilePath,
-  filterDiffAdditions,
+  filterDiffLineAdditions,
+  filterDiffFileCreations,
   hasNumberOfCodeBlocksIncreased,
 };

development/fitness-functions/common/test-data.ts

@@ -0,0 +1,40 @@
+const generateCreateFileDiff = (
+  filePath = 'file.txt',
+  content = 'Lorem ipsum',
+): string => `
+diff --git a/${filePath} b/${filePath}
+new file mode 100644
+index 000000000..30d74d258
+--- /dev/null
++++ b/${filePath}
+@@ -0,0 +1 @@
++${content}
+`;
+
+const generateModifyFilesDiff = (
+  filePath = 'file.txt',
+  addition = 'Lorem ipsum',
+  removal = '',
+): string => {
+  const additionBlock = addition
+    ? `
+@@ -1,3 +1,8 @@
++${addition}`.trim()
+    : '';
+
+  const removalBlock = removal
+    ? `
+@@ -34,33 +39,4 @@
+-${removal}`.trim()
+    : '';
+
+  return `
+diff --git a/${filePath} b/${filePath}
+index 57d5de75c..808d8ba37 100644
+--- a/${filePath}
++++ b/${filePath}
+${additionBlock}
+${removalBlock}`;
+};
+
+export { generateCreateFileDiff, generateModifyFilesDiff };

development/fitness-functions/index.js

@@ -1,53 +0,0 @@
-const fs = require('fs');
-const { execSync } = require('child_process');
-const { checkMochaSyntax } = require('./check-mocha-syntax');
-
-const AUTOMATION_TYPE = Object.freeze({
-  CI: 'ci',
-  PRE_COMMIT_HOOK: 'pre-commit-hook',
-  PRE_PUSH_HOOK: 'pre-push-hook',
-});
-
-const automationType = process.argv[2];
-
-if (automationType === AUTOMATION_TYPE.CI) {
-  const optionalArguments = process.argv.slice(3);
-  if (optionalArguments.length !== 1) {
-    console.error('Invalid number of arguments.');
-    process.exit(1);
-  }
-
-  const diff = fs.readFileSync(optionalArguments[0], {
-    encoding: 'utf8',
-    flag: 'r',
-  });
-
-  checkMochaSyntax(diff);
-} else if (automationType === AUTOMATION_TYPE.PRE_COMMIT_HOOK) {
-  const diff = getPreCommitHookDiff();
-
-  checkMochaSyntax(diff);
-} else if (automationType === AUTOMATION_TYPE.PRE_PUSH_HOOK) {
-  const diff = getPrePushHookDiff();
-
-  checkMochaSyntax(diff);
-} else {
-  console.error('Invalid automation type.');
-  process.exit(1);
-}
-
-function getPreCommitHookDiff() {
-  return execSync(`git diff --cached HEAD`).toString().trim();
-}
-
-function getPrePushHookDiff() {
-  const currentBranch = execSync(`git rev-parse --abbrev-ref HEAD`)
-    .toString()
-    .trim();
-
-  return execSync(
-    `git diff ${currentBranch} origin/${currentBranch} -- . ':(exclude)development/fitness-functions/'`,
-  )
-    .toString()
-    .trim();
-}

development/fitness-functions/index.ts

@@ -0,0 +1,11 @@
+import { AUTOMATION_TYPE } from './common/constants';
+import { getDiffByAutomationType } from './common/get-diff';
+import { IRule, RULES, runFitnessFunctionRule } from './rules';
+
+const automationType: AUTOMATION_TYPE = process.argv[2] as AUTOMATION_TYPE;
+
+const diff = getDiffByAutomationType(automationType);
+
+if (typeof diff === 'string') {
+  RULES.forEach((rule: IRule): void => runFitnessFunctionRule(rule, diff));
+}

development/fitness-functions/rules/index.ts

@@ -0,0 +1,42 @@
+import { preventSinonAssertSyntax } from './sinon-assert-syntax';
+import { preventJavaScriptFileAdditions } from './javascript-additions';
+
+const RULES: IRule[] = [
+  {
+    name: "Don't use `sinon` or `assert` in unit tests",
+    fn: preventSinonAssertSyntax,
+    docURL:
+      'https://github.com/MetaMask/metamask-extension/blob/develop/docs/testing.md#favor-jest-instead-of-mocha',
+  },
+  {
+    name: "Don't add JS or JSX files to the `shared` directory",
+    fn: preventJavaScriptFileAdditions,
+  },
+];
+
+interface IRule {
+  name: string;
+  fn: (diff: string) => boolean;
+  docURL?: string;
+}
+
+function runFitnessFunctionRule(rule: IRule, diff: string): void {
+  const { name, fn, docURL } = rule;
+  console.log(`Checking rule "${name}"...`);
+
+  const hasRulePassed: boolean = fn(diff) as boolean;
+  if (hasRulePassed === true) {
+    console.log(`...OK`);
+  } else {
+    console.log(`...FAILED. Changes not accepted by the fitness function.`);
+
+    if (docURL) {
+      console.log(`For more info: ${docURL}.`);
+    }
+
+    process.exit(1);
+  }
+}
+
+export { RULES, runFitnessFunctionRule };
+export type { IRule };

development/fitness-functions/rules/javascript-additions.test.ts

@@ -0,0 +1,51 @@
+import {
+  generateModifyFilesDiff,
+  generateCreateFileDiff,
+} from '../common/test-data';
+import { preventJavaScriptFileAdditions } from './javascript-additions';
+
+describe('preventJavaScriptFileAdditions()', (): void => {
+  it('should pass when receiving an empty diff', (): void => {
+    const testDiff = '';
+
+    const hasRulePassed = preventJavaScriptFileAdditions(testDiff);
+
+    expect(hasRulePassed).toBe(true);
+  });
+
+  it('should pass when receiving a diff with a new TS file on the shared folder', (): void => {
+    const testDiff = [
+      generateModifyFilesDiff('new-file.ts', 'foo', 'bar'),
+      generateModifyFilesDiff('old-file.js', undefined, 'pong'),
+      generateCreateFileDiff('shared/test.ts', 'yada yada yada yada'),
+    ].join('');
+
+    const hasRulePassed = preventJavaScriptFileAdditions(testDiff);
+
+    expect(hasRulePassed).toBe(true);
+  });
+
+  it('should not pass when receiving a diff with a new JS file on the shared folder', (): void => {
+    const testDiff = [
+      generateModifyFilesDiff('new-file.ts', 'foo', 'bar'),
+      generateModifyFilesDiff('old-file.js', undefined, 'pong'),
+      generateCreateFileDiff('shared/test.js', 'yada yada yada yada'),
+    ].join('');
+
+    const hasRulePassed = preventJavaScriptFileAdditions(testDiff);
+
+    expect(hasRulePassed).toBe(false);
+  });
+
+  it('should not pass when receiving a diff with a new JSX file on the shared folder', (): void => {
+    const testDiff = [
+      generateModifyFilesDiff('new-file.ts', 'foo', 'bar'),
+      generateModifyFilesDiff('old-file.js', undefined, 'pong'),
+      generateCreateFileDiff('shared/test.jsx', 'yada yada yada yada'),
+    ].join('');
+
+    const hasRulePassed = preventJavaScriptFileAdditions(testDiff);
+
+    expect(hasRulePassed).toBe(false);
+  });
+});

development/fitness-functions/rules/javascript-additions.ts

@@ -0,0 +1,18 @@
+import { SHARED_FOLDER_JS_REGEX } from '../common/constants';
+import {
+  filterDiffByFilePath,
+  filterDiffFileCreations,
+} from '../common/shared';
+
+function preventJavaScriptFileAdditions(diff: string): boolean {
+  const sharedFolderDiff = filterDiffByFilePath(diff, SHARED_FOLDER_JS_REGEX);
+  const sharedFolderCreationDiff = filterDiffFileCreations(sharedFolderDiff);
+
+  const hasCreatedAtLeastOneJSFileInShared = sharedFolderCreationDiff !== '';
+  if (hasCreatedAtLeastOneJSFileInShared) {
+    return false;
+  }
+  return true;
+}
+
+export { preventJavaScriptFileAdditions };

development/fitness-functions/rules/sinon-assert-syntax.test.ts

@@ -0,0 +1,29 @@
+import { generateModifyFilesDiff } from '../common/test-data';
+import { preventSinonAssertSyntax } from './sinon-assert-syntax';
+
+describe('preventSinonAssertSyntax()', (): void => {
+  it('should pass when receiving an empty diff', (): void => {
+    const testDiff = '';
+
+    const hasRulePassed = preventSinonAssertSyntax(testDiff);
+
+    expect(hasRulePassed).toBe(true);
+  });
+
+  it('should not pass when receiving a diff with one of the blocked expressions', (): void => {
+    const infringingExpression = 'assert.equal';
+    const testDiff = [
+      generateModifyFilesDiff('new-file.ts', 'foo', 'bar'),
+      generateModifyFilesDiff('old-file.js', undefined, 'pong'),
+      generateModifyFilesDiff(
+        'test.js',
+        `yada yada ${infringingExpression} yada yada`,
+        undefined,
+      ),
+    ].join('');
+
+    const hasRulePassed = preventSinonAssertSyntax(testDiff);
+
+    expect(hasRulePassed).toBe(false);
+  });
+});

development/fitness-functions/rules/sinon-assert-syntax.ts

@@ -0,0 +1,30 @@
+import { EXCLUDE_E2E_TESTS_REGEX } from '../common/constants';
+import {
+  filterDiffLineAdditions,
+  filterDiffByFilePath,
+  hasNumberOfCodeBlocksIncreased,
+} from '../common/shared';
+
+const codeBlocks = [
+  "import { strict as assert } from 'assert';",
+  'assert.deepEqual',
+  'assert.equal',
+  'assert.rejects',
+  'assert.strictEqual',
+  'sinon.',
+];
+
+function preventSinonAssertSyntax(diff: string): boolean {
+  const diffByFilePath = filterDiffByFilePath(diff, EXCLUDE_E2E_TESTS_REGEX);
+  const diffAdditions = filterDiffLineAdditions(diffByFilePath);
+  const hashmap = hasNumberOfCodeBlocksIncreased(diffAdditions, codeBlocks);
+
+  const haveOccurencesOfAtLeastOneCodeBlockIncreased =
+    Object.values(hashmap).includes(true);
+  if (haveOccurencesOfAtLeastOneCodeBlockIncreased) {
+    return false;
+  }
+  return true;
+}
+
+export { preventSinonAssertSyntax };

package.json

@@ -91,7 +91,7 @@
     "test-storybook": "test-storybook -c .storybook",
     "test-storybook:ci": "concurrently -k -s first -n \"SB,TEST\" -c \"magenta,blue\" \"yarn storybook:build && npx http-server storybook-build --port 6006 \" \"wait-on tcp:6006 && yarn test-storybook --maxWorkers=2\"",
     "githooks:install": "husky install",
-    "fitness-functions": "node development/fitness-functions/index.js",
+    "fitness-functions": "ts-node development/fitness-functions/index.ts",
     "generate-beta-commit": "node ./development/generate-beta-commit.js"
   },
   "resolutions": {