Support returning diff from oneline strings

CHANGELOG.md

@@ -92,6 +92,8 @@
   ([#6181](https://github.com/facebook/jest/pull/6181))
 * `[expect]` Include custom mock names in error messages
   ([#6199](https://github.com/facebook/jest/pull/6199))
+* `[jest-diff]` Support returning diff from oneline strings
+  ([#6221](https://github.com/facebook/jest/pull/6221))
 * `[expect]` Improve return matchers
   ([#6172](https://github.com/facebook/jest/pull/6172))
 

integration-tests/__tests__/__snapshots__/failures.test.js.snap

@@ -407,6 +407,9 @@ exports[`works with named snapshot failures 1`] = `
 
     Received value does not match stored snapshot \\"failing named snapshot: snapname 1\\".
 
+    - Snapshot
+    + Received
+
     - \\"bar\\"
     + \\"foo\\"
 
@@ -840,6 +843,9 @@ exports[`works with snapshot failures 1`] = `
 
     Received value does not match stored snapshot \\"failing snapshot 1\\".
 
+    - Snapshot
+    + Received
+
     - \\"bar\\"
     + \\"foo\\"
 

packages/expect/src/matchers.js

@@ -30,6 +30,7 @@ import {
   iterableEquality,
   subsetEquality,
   typeEquality,
+  isOneline,
 } from './utils';
 import {equals} from './jasmine_utils';
 
@@ -59,10 +60,8 @@ const matchers: MatchersObject = {
             getType(received) === getType(expected) &&
             (getType(received) === 'object' || getType(expected) === 'array') &&
             equals(received, expected, [iterableEquality]);
-
-          const diffString = diff(expected, received, {
-            expand: this.expand,
-          });
+          const oneline = isOneline(expected, received);
+          const diffString = diff(expected, received, {expand: this.expand});
 
           return (
             matcherHint('.toBe', undefined, undefined, {
@@ -72,7 +71,7 @@ const matchers: MatchersObject = {
             '\n\n' +
             `Expected: ${printExpected(expected)}\n` +
             `Received: ${printReceived(received)}` +
-            (diffString ? `\n\nDifference:\n\n${diffString}` : '') +
+            (diffString && !oneline ? `\n\nDifference:\n\n${diffString}` : '') +
             (suggestToEqual ? ` ${SUGGEST_TO_EQUAL}` : '')
           );
         };
@@ -375,17 +374,17 @@ const matchers: MatchersObject = {
           `Received:\n` +
           `  ${printReceived(received)}`
       : () => {
-          const diffString = diff(expected, received, {
-            expand: this.expand,
-          });
+          const oneline = isOneline(expected, received);
+          const diffString = diff(expected, received, {expand: this.expand});
+
           return (
             matcherHint('.toEqual') +
             '\n\n' +
             `Expected value to equal:\n` +
             `  ${printExpected(expected)}\n` +
             `Received:\n` +
             `  ${printReceived(received)}` +
-            (diffString ? `\n\nDifference:\n\n${diffString}` : '')
+            (diffString && !oneline ? `\n\nDifference:\n\n${diffString}` : '')
           );
         };
 

packages/expect/src/spy_matchers.js

@@ -24,7 +24,7 @@ import {
   RECEIVED_COLOR,
 } from 'jest-matcher-utils';
 import {equals} from './jasmine_utils';
-import {iterableEquality, partition} from './utils';
+import {iterableEquality, partition, isOneline} from './utils';
 import diff from 'jest-diff';
 
 const createToBeCalledMatcher = matcherName => (received, expected) => {
@@ -555,12 +555,13 @@ const formatMismatchedArgs = (expected, received) => {
   const printedArgs = [];
   for (let i = 0; i < length; i++) {
     if (!equals(expected[i], received[i], [iterableEquality])) {
+      const oneline = isOneline(expected[i], received[i]);
       const diffString = diff(expected[i], received[i]);
       printedArgs.push(
         `  ${printExpected(expected[i])}\n` +
           `as argument ${i + 1}, but it was called with\n` +
           `  ${printReceived(received[i])}.` +
-          (diffString ? `\n\nDifference:\n\n${diffString}` : ''),
+          (diffString && !oneline ? `\n\nDifference:\n\n${diffString}` : ''),
       );
     } else if (i >= expected.length) {
       printedArgs.push(

packages/expect/src/utils.js

@@ -221,3 +221,10 @@ export const isError = (value: any) => {
 export function emptyObject(obj: any) {
   return obj && typeof obj === 'object' ? !Object.keys(obj).length : false;
 }
+
+const MULTILINE_REGEXP = /[\r\n]/;
+
+export const isOneline = (expected: any, received: any) =>
+  typeof expected === 'string' &&
+  typeof received === 'string' &&
+  (!MULTILINE_REGEXP.test(expected) || !MULTILINE_REGEXP.test(received));

packages/jest-diff/src/__tests__/__snapshots__/diff.test.js.snap

@@ -208,3 +208,37 @@ exports[`highlight only the last in odd length of leading spaces (expanded) 1`]
 <red>+ }, {});</>
 <dim>  </pre></>"
 `;
+
+exports[`oneline strings 1`] = `
+"<green>- Expected</>
+<red>+ Received</>
+
+<green>- ab</>
+<red>+ aa</>"
+`;
+
+exports[`oneline strings 2`] = `
+"<green>- Expected</>
+<red>+ Received</>
+
+<green>- 123456789</>
+<red>+ 234567890</>"
+`;
+
+exports[`oneline strings 3`] = `
+"<green>- Expected</>
+<red>+ Received</>
+
+<green>- oneline</>
+<red>+ multi</>
+<red>+ line</>"
+`;
+
+exports[`oneline strings 4`] = `
+"<green>- Expected</>
+<red>+ Received</>
+
+<green>- multi</>
+<green>- line</>
+<red>+ oneline</>"
+`;

packages/jest-diff/src/__tests__/diff.test.js

@@ -82,12 +82,10 @@ describe('no visual difference', () => {
 });
 
 test('oneline strings', () => {
-  // oneline strings don't produce a diff currently.
-  expect(diff('ab', 'aa')).toBe(null);
-  expect(diff('123456789', '234567890')).toBe(null);
-  // if either string is oneline
-  expect(diff('oneline', 'multi\nline')).toBe(null);
-  expect(diff('multi\nline', 'oneline')).toBe(null);
+  expect(diff('ab', 'aa')).toMatchSnapshot();
+  expect(diff('123456789', '234567890')).toMatchSnapshot();
+  expect(diff('oneline', 'multi\nline')).toMatchSnapshot();
+  expect(diff('multi\nline', 'oneline')).toMatchSnapshot();
 });
 
 describe('falls back to not call toJSON', () => {

packages/jest-diff/src/diff_strings.js

@@ -9,8 +9,8 @@
 
 import chalk from 'chalk';
 import {diffLines, structuredPatch} from 'diff';
-
 import {NO_DIFF_MESSAGE} from './constants.js';
+
 const DIFF_CONTEXT_DEFAULT = 5;
 
 export type DiffOptions = {|

packages/jest-diff/src/index.js

@@ -47,8 +47,6 @@ const FALLBACK_FORMAT_OPTIONS_0 = Object.assign({}, FALLBACK_FORMAT_OPTIONS, {
   indent: 0,
 });
 
-const MULTILINE_REGEXP = /[\r\n]/;
-
 // Generate a string that will highlight the difference between two values
 // with green and red. (similar to how github does code diffing)
 function diff(a: any, b: any, options: ?DiffOptions): ?string {
@@ -88,11 +86,7 @@ function diff(a: any, b: any, options: ?DiffOptions): ?string {
 
   switch (aType) {
     case 'string':
-      const multiline = MULTILINE_REGEXP.test(a) && b.indexOf('\n') !== -1;
-      if (multiline) {
-        return diffStrings(a, b, options);
-      }
-      return null;
+      return diffStrings(a, b, options);
     case 'number':
     case 'boolean':
       return null;