Allow for setting the annotation for strings (#15)

Author: Kent C. Dodds

README.md

@@ -135,6 +135,9 @@ expect(valueA: any).toMatchDiffSnapshot(valueB: any, options?: Options) => void
 * `expand: boolean` (default: `false`) – expand the diff, so the whole information is preserved
 * `colors: boolean` (default: `false`) – preserve color information from Jest diff
 * `contextLines: number` (default: 5) - number of context lines to be shown at the beginning and at the end of a snapshot
+* `aAnnotation: string` (default: `'First Value'`) - the annotation indicating from which serialization the `-` lines are
+* `bAnnotation: string` (default: `'Second Value'`) - the annotation indicating from which serialization the `+` lines are
+
 
 ---
 

__tests__/getSnapshotDiffSerializer.test.js

@@ -1,7 +1,7 @@
 // @flow
 
 const snapshotDiff = require('../src/index');
-
+// $FlowFixMe – wrong type declaration in flow-typed/jest@20.x.x
 expect.addSnapshotSerializer(snapshotDiff.getSnapshotDiffSerializer());
 
 test('serialize text diff output', () => {

src/index.js

@@ -13,12 +13,16 @@ type Options = {
   expand?: boolean,
   colors?: boolean,
   contextLines?: number,
+  aAnnotation?: string,
+  bAnnotation?: string,
 };
 
 const defaultOptions = {
   expand: false,
   colors: false,
   contextLines: -1, // Forces to use default from Jest
+  aAnnotation: 'First value',
+  bAnnotation: 'Second value',
 };
 
 const SNAPSHOT_TITLE = 'Snapshot Diff:\n';
@@ -49,8 +53,8 @@ function diffStrings(valueA: any, valueB: any, options: Options) {
   return diff(valueA, valueB, {
     expand: options.expand,
     contextLines: options.contextLines,
-    aAnnotation: 'First value',
-    bAnnotation: 'Second value',
+    aAnnotation: options.aAnnotation,
+    bAnnotation: options.bAnnotation,
   });
 }