fix(preset): createJestPreset fails with base and no array

If no moduleFileExtensions or testMatch is given to the createJestPreset
it'd fail

Author: huafu

src/config/create-jest-preset.spec.ts

@@ -31,3 +31,46 @@ it('should return correct defaults when allowJs is true', () => {
     },
   })
 })
+
+it('should be able to use a base config', () => {
+  expect(createJestPreset(undefined, {})).toMatchInlineSnapshot(`
+Object {
+  "moduleFileExtensions": Array [
+    "js",
+    "json",
+    "jsx",
+    "node",
+    "ts",
+    "tsx",
+  ],
+  "testMatch": Array [
+    "**/__tests__/**/*.js?(x)",
+    "**/?(*.)+(spec|test).js?(x)",
+    "**/__tests__/**/*.ts?(x)",
+    "**/?(*.)+(spec|test).ts?(x)",
+  ],
+  "transform": Object {
+    "^.+\\\\.tsx?$": "ts-jest",
+  },
+}
+`)
+  expect(createJestPreset(undefined, { testMatch: ['foo'], moduleFileExtensions: ['bar'], transform: { foo: 'bar' } }))
+    .toMatchInlineSnapshot(`
+Object {
+  "moduleFileExtensions": Array [
+    "bar",
+    "ts",
+    "tsx",
+  ],
+  "testMatch": Array [
+    "foo",
+    "**/__tests__/**/*.ts?(x)",
+    "**/?(*.)+(spec|test).ts?(x)",
+  ],
+  "transform": Object {
+    "^.+\\\\.tsx?$": "ts-jest",
+    "foo": "bar",
+  },
+}
+`)
+})

src/config/create-jest-preset.ts

@@ -12,18 +12,16 @@ const defaults = jestConfig.defaults || {
   moduleFileExtensions: ['js', 'json', 'jsx', 'node'],
 }
 
-export function createJestPreset(
-  { allowJs = false }: CreateJestPresetOptions = {},
-  from: jest.InitialOptions = defaults,
-) {
+export function createJestPreset({ allowJs = false }: CreateJestPresetOptions = {}, from?: jest.InitialOptions) {
   logger.debug({ allowJs }, 'creating jest presets', allowJs ? 'handling' : 'not handling', 'JavaScript files')
+  from = { ...defaults, ...from }
   return {
     transform: {
       ...from.transform,
       [allowJs ? '^.+\\.[tj]sx?$' : '^.+\\.tsx?$']: 'ts-jest',
     },
-    testMatch: dedup([...from.testMatch, '**/__tests__/**/*.ts?(x)', '**/?(*.)+(spec|test).ts?(x)']),
-    moduleFileExtensions: dedup([...from.moduleFileExtensions, 'ts', 'tsx']),
+    testMatch: dedup([...(from.testMatch || []), '**/__tests__/**/*.ts?(x)', '**/?(*.)+(spec|test).ts?(x)']),
+    moduleFileExtensions: dedup([...(from.moduleFileExtensions || []), 'ts', 'tsx']),
   }
 }