Allow skip process method if createTransformer definded

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ### Features
 
+* `[jest-runtime]` Allow for transform plugins to skip the definition process
+  method if createTransformer method was defined.
+  ([#5999](https://github.com/facebook/jest/pull/5999))
 * `[expect]` Add stack trace for async errors
   ([#6008](https://github.com/facebook/jest/pull/6008))
 * `[jest-jasmine2]` Add stack trace for timeouts

packages/jest-runtime/src/__tests__/script_transformer.test.js

@@ -85,6 +85,44 @@ jest.mock(
   {virtual: true},
 );
 
+// Bad preprocessor
+jest.mock(
+  'skipped-required-props-preprocessor',
+  () => {
+    return {};
+  },
+  {virtual: true},
+);
+
+// Bad preprocessor
+jest.mock(
+  'skipped-required-create-transformer-props-preprocessor',
+  () => {
+    return {
+      createTransformer() {
+        return {};
+      },
+    };
+  },
+  {virtual: true},
+);
+
+jest.mock(
+  'skipped-process-method-preprocessor',
+  () => {
+    return {
+      createTransformer() {
+        const mockProcess = jest.fn();
+        mockProcess.mockReturnValue('code');
+        return {
+          process: mockProcess,
+        };
+      },
+    };
+  },
+  {virtual: true},
+);
+
 const getCachePath = (fs, config) => {
   for (const path in mockFs) {
     if (path.startsWith(config.cacheDirectory)) {
@@ -262,6 +300,38 @@ describe('ScriptTransformer', () => {
     },
   );
 
+  it("throws an error if `process` doesn't defined", () => {
+    Object.assign(config, {
+      transform: [['^.+\\.js$', 'skipped-required-props-preprocessor']],
+    });
+    const scriptTransformer = new ScriptTransformer(config);
+    expect(() =>
+      scriptTransformer.transformSource('sample.js', '', false),
+    ).toThrow('Jest: a transform must export a `process` function.');
+  });
+
+  it('throws an error if createTransformer returns object without `process` method', () => {
+    Object.assign(config, {
+      transform: [
+        ['^.+\\.js$', 'skipped-required-create-transformer-props-preprocessor'],
+      ],
+    });
+    const scriptTransformer = new ScriptTransformer(config);
+    expect(() =>
+      scriptTransformer.transformSource('sample.js', '', false),
+    ).toThrow('Jest: a transform must export a `process` function.');
+  });
+
+  it("shouldn't throw error without process method. But with corrent createTransformer method", () => {
+    Object.assign(config, {
+      transform: [['^.+\\.js$', 'skipped-process-method-preprocessor']],
+    });
+    const scriptTransformer = new ScriptTransformer(config);
+    expect(() =>
+      scriptTransformer.transformSource('sample.js', '', false),
+    ).not.toThrow();
+  });
+
   it('uses the supplied preprocessor', () => {
     config = Object.assign(config, {
       transform: [['^.+\\.js$', 'test_preprocessor']],

packages/jest-runtime/src/script_transformer.js

@@ -137,14 +137,14 @@ export default class ScriptTransformer {
 
       // $FlowFixMe
       transform = (require(transformPath): Transformer);
+      if (typeof transform.createTransformer === 'function') {
+        transform = transform.createTransformer();
+      }
       if (typeof transform.process !== 'function') {
         throw new TypeError(
           'Jest: a transform must export a `process` function.',
         );
       }
-      if (typeof transform.createTransformer === 'function') {
-        transform = transform.createTransformer();
-      }
       this._transformCache.set(transformPath, transform);
     }
     return transform;