feat: Allow custom serializers through setSerializers

Provides new setSerializers function to set the serializer objects to
be used before diffing. React component serializer implementation using
`react-test-renderer` has been extracted out.

Fixes #18
Fixes #30
Fixes #31

Author: alistairjcbrown

README.md

@@ -93,6 +93,45 @@ exports[`snapshot difference between 2 React components state 1`] = `
 `;
 ```
 
+## Custom serializers
+
+By default, `snapshot-diff` uses a built in React serializer based on `react-test-renderer`. The
+[serializers](https://jestjs.io/docs/en/configuration#snapshotserializers-array-string) used can be set by calling
+`setSerializers` with an array of serializers to use. The order of serializers in this array may be important to you as
+serializers are tested in order until a match is found.
+
+`setSerializers` can be used to add new serializers for unsupported data types, or to set a different serializer
+for React components. If you want to keep the default React serializer in place, don't forget to add the default
+serializers to your list of serializers!
+
+### Adding a new custom serializer
+
+```js
+const snapshotDiff = require('snapshot-diff');
+const myCustomSerializer = require('./my-custom-serializer');
+
+snapshotDiff.setSerializers([
+  ...snapshotDiff.defaultSerializers, // use default React serializer - add this if you want to serialise React components!
+  myCustomSerializer
+]);
+```
+
+### Serializing React components with a different serializer
+
+You can replace the default React serializer by omitting it from the serializer list. The following uses enzymes to-json
+serializer instead:
+
+```js
+const snapshotDiff = require('snapshot-diff');
+const enzymeToJson = require('enzyme-to-json/serializer');
+const myCustomSerializer = require('./my-custom-serializer');
+
+snapshotDiff.setSerializers([
+  enzymeToJson, // using enzymes serializer instead
+  myCustomSerializer
+]);
+```
+
 ## Snapshot serializer
 
 By default Jest adds extra quotes around strings so it makes diff snapshots of objects too noisy.

__tests__/__snapshots__/setSerializers.test.js.snap

@@ -0,0 +1,107 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`default rendered components can use contextLines 1`] = `
+"Snapshot Diff:
+- <NestedComponent test=\\"say\\" />
++ <NestedComponent test=\\"my name\\" />
+
+@@ -4,1 +4,1 @@
+-     say
++     my name"
+`;
+
+exports[`default rendered components diffs components 1`] = `
+"Snapshot Diff:
+- <NestedComponent test=\\"say\\" />
++ <NestedComponent test=\\"my name\\" />
+
+@@ -1,9 +1,9 @@
+  <div>
+    <span>
+      Hello World - 
+-     say
++     my name
+    </span>
+    <div>
+      I have value 
+      1234
+    </div>"
+`;
+
+exports[`enzyme shallow rendered components can use contextLines 1`] = `
+"Snapshot Diff:
+- First value
++ Second value
+
+@@ -4,1 +4,1 @@
+-     say
++     my name"
+`;
+
+exports[`enzyme shallow rendered components diffs components 1`] = `
+"Snapshot Diff:
+- First value
++ Second value
+
+  <div>
+    <span>
+      Hello World - 
+-     say
++     my name
+    </span>
+    <Component
+      value={1234}
+    />
+  </div>"
+`;
+
+exports[`react test-renderer shallow rendered components can use contextLines 1`] = `
+"Snapshot Diff:
+- <div><span>Hello World - say</span><Component value={1234} /></div>
++ <div><span>Hello World - my name</span><Component value={1234} /></div>
+
+@@ -4,1 +4,1 @@
+-     say
++     my name"
+`;
+
+exports[`react test-renderer shallow rendered components diffs components 1`] = `
+"Snapshot Diff:
+- <div><span>Hello World - say</span><Component value={1234} /></div>
++ <div><span>Hello World - my name</span><Component value={1234} /></div>
+
+@@ -1,9 +1,9 @@
+  <div>
+    <span>
+      Hello World - 
+-     say
++     my name
+    </span>
+    <div>
+      I have value 
+      1234
+    </div>"
+`;
+
+exports[`values which are not components can use contextLines 1`] = `
+"Snapshot Diff:
+- First value
++ Second value
+
+@@ -3,1 +3,1 @@
+-   \\"hello\\": \\"world\\",
++   \\"hello\\": \\"there\\","
+`;
+
+exports[`values which are not components diffs objects 1`] = `
+"Snapshot Diff:
+- First value
++ Second value
+
+  Object {
+    \\"foo\\": \\"bar\\",
+-   \\"hello\\": \\"world\\",
++   \\"hello\\": \\"there\\",
+    \\"testing\\": 123,
+  }"
+`;

__tests__/setSerializers.test.js

@@ -0,0 +1,117 @@
+// @flow
+const React = require('react');
+const { configure, shallow: enzymeShallow } = require('enzyme');
+const ReactShallowRenderer = require('react-test-renderer/shallow');
+const Adapter = require('enzyme-adapter-react-16');
+const enzymeToJson = require('enzyme-to-json/serializer');
+const snapshotDiff = require('../src/index');
+
+configure({ adapter: new Adapter() });
+const reactShallow = new ReactShallowRenderer();
+
+snapshotDiff.setSerializers([...snapshotDiff.defaultSerializers, enzymeToJson]);
+
+type Props = {
+  test: string,
+};
+
+const Component = ({ value }) => <div>I have value {value}</div>;
+
+const NestedComponent = (props: Props) => (
+  <div>
+    <span>Hello World - {props.test}</span>
+    <Component value={1234} />
+  </div>
+);
+
+describe('default rendered components', () => {
+  test('diffs components', () => {
+    expect(
+      snapshotDiff(
+        <NestedComponent test="say" />,
+        <NestedComponent test="my name" />
+      )
+    ).toMatchSnapshot();
+  });
+
+  test('can use contextLines', () => {
+    expect(
+      snapshotDiff(
+        <NestedComponent test="say" />,
+        <NestedComponent test="my name" />,
+        {
+          contextLines: 0,
+        }
+      )
+    ).toMatchSnapshot();
+  });
+});
+
+describe('enzyme shallow rendered components', () => {
+  test('diffs components', () => {
+    expect(
+      snapshotDiff(
+        enzymeShallow(<NestedComponent test="say" />),
+        enzymeShallow(<NestedComponent test="my name" />)
+      )
+    ).toMatchSnapshot();
+  });
+
+  test('can use contextLines', () => {
+    expect(
+      snapshotDiff(
+        enzymeShallow(<NestedComponent test="say" />),
+        enzymeShallow(<NestedComponent test="my name" />),
+        {
+          contextLines: 0,
+        }
+      )
+    ).toMatchSnapshot();
+  });
+});
+
+describe('react test-renderer shallow rendered components', () => {
+  test('diffs components', () => {
+    expect(
+      snapshotDiff(
+        reactShallow.render(<NestedComponent test="say" />),
+        reactShallow.render(<NestedComponent test="my name" />)
+      )
+    ).toMatchSnapshot();
+  });
+
+  test('can use contextLines', () => {
+    expect(
+      snapshotDiff(
+        reactShallow.render(<NestedComponent test="say" />),
+        reactShallow.render(<NestedComponent test="my name" />),
+        {
+          contextLines: 0,
+        }
+      )
+    ).toMatchSnapshot();
+  });
+});
+
+describe('values which are not components', () => {
+  test('diffs objects', () => {
+    expect(
+      snapshotDiff(
+        { foo: 'bar', hello: 'world', testing: 123 },
+        { foo: 'bar', hello: 'there', testing: 123 }
+      )
+    ).toMatchSnapshot();
+  });
+
+  test('can use contextLines', () => {
+    expect(
+      snapshotDiff(
+        { foo: 'bar', hello: 'world', testing: 123 },
+        { foo: 'bar', hello: 'there', testing: 123 },
+        {
+          contextLines: 0,
+        }
+      )
+    ).toMatchSnapshot();
+  });
+});

extend-expect.js

@@ -1,3 +1,4 @@
+/* global expect */
 const { toMatchDiffSnapshot } = require('./build/');
 
-expect.extend({ toMatchDiffSnapshot });
+expect.extend({ toMatchDiffSnapshot });

package.json

@@ -30,11 +30,15 @@
     "@babel/preset-env": "^7.0.0",
     "@babel/preset-flow": "^7.0.0",
     "@babel/preset-react": "^7.0.0",
+    "enzyme": "^3.10.0",
+    "enzyme-adapter-react-16": "^1.14.0",
+    "enzyme-to-json": "^3.4.0",
     "eslint": "^5.15.3",
     "eslint-config-callstack-io": "^1.1.1",
     "flow-bin": "^0.102.0",
     "jest": "^24.0.0",
     "react": "^16.7.0",
+    "react-dom": "16.7.0",
     "react-test-renderer": "^16.7.0"
   }
 }

src/index.js

@@ -4,10 +4,7 @@
 
 const diff = require('jest-diff');
 const snapshot = require('jest-snapshot');
-const prettyFormat = require('pretty-format');
-
-const { ReactElement } = prettyFormat.plugins;
-const reactElement = Symbol.for('react.element');
+const reactSerializer = require('./react-serializer');
 
 type Options = {|
   expand?: boolean,
@@ -29,12 +26,27 @@ const defaultOptions = {
 
 const SNAPSHOT_TITLE = 'Snapshot Diff:\n';
 
+const identity = value => value;
+const defaultSerializers = [reactSerializer];
+let serializers = defaultSerializers;
+
 const snapshotDiff = (valueA: any, valueB: any, options?: Options): string => {
   let difference;
   const mergedOptions = { ...defaultOptions, ...options };
 
-  if (isReactComponent(valueA) && isReactComponent(valueB)) {
-    difference = diffReactComponents(valueA, valueB, mergedOptions);
+  const matchingSerializer = serializers.find(
+    ({ test }) => test(valueA) && test(valueB)
+  );
+
+  if (matchingSerializer) {
+    const { print, diffOptions } = matchingSerializer;
+    const serializerOptions = diffOptions
+      ? diffOptions(valueA, valueB) || {}
+      : {};
+    difference = diffStrings(print(valueA, identity), print(valueB, identity), {
+      ...mergedOptions,
+      ...serializerOptions,
+    });
   } else {
     difference = diffStrings(valueA, valueB, mergedOptions);
   }
@@ -55,9 +67,6 @@ const snapshotDiff = (valueA: any, valueB: any, options?: Options): string => {
   return SNAPSHOT_TITLE + difference;
 };
 
-const isReactComponent = (value: any) =>
-  value && value.$$typeof === reactElement;
-
 function diffStrings(valueA: any, valueB: any, options: Options) {
   return diff(valueA, valueB, {
     expand: options.expand,
@@ -67,36 +76,6 @@ function diffStrings(valueA: any, valueB: any, options: Options) {
   });
 }
 
-function requireReactTestRenderer() {
-  try {
-    return require('react-test-renderer'); // eslint-disable-line import/no-extraneous-dependencies
-  } catch (error) {
-    if (error.code === 'MODULE_NOT_FOUND') {
-      throw new Error(
-        `Failed to load optional module "react-test-renderer". ` +
-          `If you need to compare React elements, please add "react-test-renderer" to your ` +
-          `project's dependencies.\n` +
-          `${error.message}`
-      );
-    }
-    throw error;
-  }
-}
-
-function diffReactComponents(valueA: any, valueB: any, options: Options) {
-  const renderer = requireReactTestRenderer();
-  const reactValueA = renderer.create(valueA).toJSON();
-  const reactValueB = renderer.create(valueB).toJSON();
-  const prettyFormatOptions = { plugins: [ReactElement], min: true };
-
-  return diff(reactValueA, reactValueB, {
-    expand: options.expand,
-    contextLines: options.contextLines,
-    aAnnotation: prettyFormat(valueA, prettyFormatOptions),
-    bAnnotation: prettyFormat(valueB, prettyFormatOptions),
-  });
-}
-
 function toMatchDiffSnapshot(
   valueA: any,
   valueB: any,
@@ -119,7 +98,13 @@ function getSnapshotDiffSerializer() {
   };
 }
 
+function setSerializers(customSerializers) {
+  serializers = customSerializers;
+}
+
 module.exports = snapshotDiff;
 module.exports.snapshotDiff = snapshotDiff;
 module.exports.toMatchDiffSnapshot = toMatchDiffSnapshot;
 module.exports.getSnapshotDiffSerializer = getSnapshotDiffSerializer;
+module.exports.setSerializers = setSerializers;
+module.exports.defaultSerializers = defaultSerializers;