tests: added run prettier tests

packages/utils/__tests__/run-prettier.test.ts

@@ -0,0 +1,42 @@
+'use strict';
+
+import fs from 'fs';
+import path from 'path';
+//eslint-disable-next-line node/no-extraneous-import
+import rimraf from 'rimraf';
+import { runPrettier } from '../src/run-prettier';
+
+const outputPath = path.join(__dirname, 'test-assets');
+const outputFile = path.join(outputPath, 'test.js');
+const stdoutSpy = jest.spyOn(process.stdout, 'write');
+
+describe('runPrettier', () => {
+    beforeEach(() => {
+        rimraf.sync(outputPath);
+        fs.mkdirSync(outputPath);
+        stdoutSpy.mockClear();
+    });
+
+    afterAll(() => {
+        rimraf.sync(outputPath);
+    });
+
+    it('should run prettier on JS string and write file', () => {
+        runPrettier(outputFile, 'console.log("1");console.log("2");');
+        expect(fs.existsSync(outputFile)).toBeTruthy();
+        const data = fs.readFileSync(outputFile, 'utf8');
+        expect(data).toContain("console.log('1');\n");
+
+        expect(stdoutSpy.mock.calls.length).toEqual(0);
+    });
+
+    it('prettier should fail on invalid JS, with file still written', () => {
+        runPrettier(outputFile, '"');
+        expect(fs.existsSync(outputFile)).toBeTruthy();
+        const data = fs.readFileSync(outputFile, 'utf8');
+        expect(data).toContain('"');
+
+        expect(stdoutSpy.mock.calls.length).toEqual(1);
+        expect(stdoutSpy.mock.calls[0][0]).toContain('WARNING: Could not apply prettier');
+    });
+});