add initial implementation

.editorconfig

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+# EditorConfig helps developers define and maintain consistent
+# coding styles between different editors and IDEs
+# editorconfig.org
+
+root = true
+
+[*]
+end_of_line = lf
+charset = utf-8
+insert_final_newline = true
+indent_style = space
+indent_size = 2
+
+[*.hbs]
+insert_final_newline = false
+
+[*.{diff,md}]
+trim_trailing_whitespace = false

.eslintrc.cjs

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+module.exports = {
+  "env": {
+    "es2021": true,
+    "node": true
+  },
+  "extends": "eslint:recommended",
+  "overrides": [{
+    files: 'test/**/*.js',
+    env: {
+      mocha: true,
+    }
+  }],
+  "parserOptions": {
+    "ecmaVersion": "latest",
+    "sourceType": "module"
+  },
+  "rules": {
+  }
+}

.github/workflows/ci.yml

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+name: Node.js CI
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        node-version: [14.x, 16.x, 18.x]
+      fail-fast: false
+
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/setup-node@v3
+        with:
+          node-version: ${{ matrix.node-version }}
+      - run: npm i -g npm@latest
+      - run: npm ci
+      - run: npm test

.gitignore

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+/node_modules/

README.md

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+# compare-fixture
+
+This is a super simple tool to compare two folders. It is intended to be used to test build systems where you have a known expected output (a fixture) that you want to compare a build process against. 
+
+## Installation
+
+You can use this tool directly with npx and not install it as follows: 
+
+```
+npx compare-fixture
+```
+
+or you can install it locally to make sure that you don't need to install it before use: 
+
+```
+npm i --save-dev compare-fixture
+```
+
+## Usage
+
+```
+npx compare-fixture <fixture folder> <comaprison folder>
+```
+
+This will test each file in `<fixture folder>` against each corresponding file in the `<comparison folder>` 
+
+**Note:** if any extra files exist in `<comparison folder>` that is **not considered an error**. This allows you to easily test a sub-section of your files with a sparse fixture. On the other hand, if a file exists in the fixture but is missing in the comparison folder then that is considered an error.
+
+## Example output
+
+```
+thing.js is different in the fixture 🚨
+
++ expected - actual
+
+  function aVeryNiceTestFunction() {
+-  console.log('I really should impolement something here');
+-  console.log('I really should impolement something here');
+-  console.log('I really should impolement something here');
+-  console.log('I really should impolement something here');
+-  console.log('I really should impolement something here');
++  console.log('I really should implement something here');
++  console.log('I really should implement something here');
+  }
+
+  function badlyIndented() {
+    let items = [
+      'one',
+-      'two',
++    'two',
+      'three',
+-  'four',
+-    'five'
++    'four',
++    'five',
+    ];
+  }
+-
+-function possiblyMissing() {
+-  console.log('a very important function');
+-}
+```
+
+And if your terminal supports colours it will output the diff with colours: 
+
+<img width="715" alt="Screenshot 2023-03-19 at 16 25 18" src="https://user-images.githubusercontent.com/594890/226189889-3151b7fb-dbf6-4889-8b22-46b58dea26d6.png">
+

index.js

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+import walkSync from 'walk-sync';
+import { readFileSync } from 'fs';
+import { join } from 'path';
+
+import { generateDiff } from 'mocha-diff';
+
+const fixtureDir = process.argv[2];
+const comparisonDir = process.argv[3];
+
+if (!fixtureDir) {
+  console.error('You need to provide the path to a fixture and to the comparison dir');
+  process.exit(1);
+}
+
+if (!comparisonDir) {
+  console.error('You need to provide the path to the comparison dir');
+  process.exit(1);
+}
+
+const fixtureFiles = walkSync(fixtureDir, { directories: false });
+
+fixtureFiles.forEach((file) => {
+  const compareFile = readFileSync(join(comparisonDir, file), 'utf8');
+  const fixtureFile = readFileSync(join(fixtureDir, file), 'utf8');
+
+  if (compareFile != fixtureFile) {
+    console.log(`${file} is different in the fixture 🚨`);
+    console.log(generateDiff(compareFile, fixtureFile));
+  }
+})