fix: babel-config + adds test

src/__helpers__/fakers.ts

@@ -1,4 +1,4 @@
-import { TsJestGlobalOptions } from '../types';
+import { TsJestGlobalOptions, BabelConfig } from '../types';
 import { resolve } from 'path';
 
 export function filePath(relPath: string): string {
@@ -29,7 +29,7 @@ describe('hello', function () {
 export function htmlSource() {
   return `
 <div>
-  <span>some text with \`backtilt\`</span>
+  <span>some text with \`backtick\`</span>
 </div>
 `;
 }
@@ -71,3 +71,11 @@ export function jestConfig<T extends jest.ProjectConfig>(
   }
   return res;
 }
+
+export function babelConfig<T extends BabelConfig>(options?: BabelConfig): T {
+  return {
+    ...options,
+    presets: [...(options && options.presets)],
+    plugins: [...(options && options.plugins)],
+  } as any;
+}

src/utils/babel-config.spec.ts

@@ -0,0 +1,53 @@
+import * as fakers from '../__helpers__/fakers';
+import * as babelCfg from './babel-config';
+import { BabelConfig } from '../types';
+
+describe('extend', () => {
+  let base!: BabelConfig;
+
+  beforeEach(() => {
+    base = fakers.babelConfig({
+      presets: ['preset-1'],
+      plugins: ['plugin-1'],
+      minified: true,
+    });
+  });
+
+  it('should be a copy', () => {
+    const extended = babelCfg.extend(base);
+    expect(extended).toEqual(base);
+    expect(extended).not.toBe(base);
+    expect(extended.presets).not.toBe(base.presets);
+    expect(extended.plugins).not.toBe(base.plugins);
+  });
+
+  it('should extend correctly', () => {
+    const extension: BabelConfig = {
+      minified: false,
+      envName: 'test',
+      plugins: ['plugin-2'],
+      presets: ['preset-2'],
+    };
+    const extended = babelCfg.extend(base, extension);
+    expect(extended).not.toBe(base);
+    expect(extended).not.toBe(extension);
+    expect(extended.presets).not.toBe(base.presets);
+    expect(extended.presets).not.toBe(extension.presets);
+    expect(extended.plugins).not.toBe(base.plugins);
+    expect(extended.plugins).not.toBe(extension.plugins);
+    expect(extended).toMatchInlineSnapshot(`
+Object {
+  "envName": "test",
+  "minified": false,
+  "plugins": Array [
+    "plugin-1",
+    "plugin-2",
+  ],
+  "presets": Array [
+    "preset-1",
+    "preset-2",
+  ],
+}
+`);
+  });
+});

src/utils/babel-config.ts

@@ -31,10 +31,13 @@ export function extend(
   // tslint:disable-next-line:trailing-comma
   ...others: BabelConfig[]
 ): BabelConfig {
-  const res = Object.assign(base, extend, ...others, {
+  const res = {
+    ...base,
+    ...extend,
+    ...others,
     presets: base.presets ? base.presets.slice() : [],
-    plugins: extend.plugins ? extend.plugins.slice() : [],
-  });
+    plugins: base.plugins ? base.plugins.slice() : [],
+  };
   others.unshift(extend);
   others.forEach(other => {
     if (other.presets) {