Improve toWarnDev matcher DX for unexpected warnings (facebook#12082)

Use jest-diff to format the warnings in a way that makes it easier to spot the differences.

package.json

@@ -70,6 +70,7 @@
     "gzip-size": "^3.0.0",
     "jasmine-check": "^1.0.0-rc.0",
     "jest": "^22.0.6",
+    "jest-diff": "^22.1.0",
     "merge-stream": "^1.0.0",
     "minimatch": "^3.0.4",
     "minimist": "^1.2.0",

scripts/jest/matchers/toWarnDev.js

@@ -1,5 +1,7 @@
 'use strict';
 
+const jestDiff = require('jest-diff');
+
 function normalizeCodeLocInfo(str) {
   return str && str.replace(/at .+?:\d+/g, 'at **');
 }
@@ -39,13 +41,19 @@ const createMatcherFor = consoleMethod =>
           }
         }
 
-        let errorMessage = `Unexpected warning recorded:\n${this.utils.printReceived(
-          message
-        )}`;
-        if (expectedMessages.length > 0) {
-          errorMessage += `\n\nThe following expected warnings were not yet seen:\n${expectedMessages
-            .map(unformatted => this.utils.printExpected(unformatted))
-            .join('\n')}`;
+        let errorMessage;
+        if (expectedMessages.length === 0) {
+          errorMessage =
+            'Unexpected warning recorded: ' +
+            this.utils.printReceived(normalizedMessage);
+        } else if (expectedMessages.length === 1) {
+          errorMessage =
+            'Unexpected warning recorded: ' +
+            jestDiff(normalizedMessage, expectedMessages[0]);
+        } else {
+          errorMessage =
+            'Unexpected warning recorded: ' +
+            jestDiff([normalizedMessage], expectedMessages);
         }
 
         // Record the call stack for unexpected warnings.

yarn.lock

@@ -3213,6 +3213,15 @@ jest-diff@^22.0.6:
     jest-get-type "^22.0.6"
     pretty-format "^22.0.6"
 
+jest-diff@^22.1.0:
+  version "22.1.0"
+  resolved "https://registry.yarnpkg.com/jest-diff/-/jest-diff-22.1.0.tgz#0fad9d96c87b453896bf939df3dc8aac6919ac38"
+  dependencies:
+    chalk "^2.0.1"
+    diff "^3.2.0"
+    jest-get-type "^22.1.0"
+    pretty-format "^22.1.0"
+
 jest-docblock@^22.0.6:
   version "22.0.6"
   resolved "https://registry.yarnpkg.com/jest-docblock/-/jest-docblock-22.0.6.tgz#f187fb2c67eec0999e569d563092125283084f9e"
@@ -3238,6 +3247,10 @@ jest-get-type@^22.0.6:
   version "22.0.6"
   resolved "https://registry.yarnpkg.com/jest-get-type/-/jest-get-type-22.0.6.tgz#301fbc0760779fdbad37b6e3239a3c1811aa75cb"
 
+jest-get-type@^22.1.0:
+  version "22.1.0"
+  resolved "https://registry.yarnpkg.com/jest-get-type/-/jest-get-type-22.1.0.tgz#4e90af298ed6181edc85d2da500dbd2753e0d5a9"
+
 jest-haste-map@^22.0.6:
   version "22.0.6"
   resolved "https://registry.yarnpkg.com/jest-haste-map/-/jest-haste-map-22.0.6.tgz#198d665f65e1c484fef106a3c970c5b47903647e"
@@ -4273,6 +4286,13 @@ pretty-format@^22.0.6:
     ansi-regex "^3.0.0"
     ansi-styles "^3.2.0"
 
+pretty-format@^22.1.0:
+  version "22.1.0"
+  resolved "https://registry.yarnpkg.com/pretty-format/-/pretty-format-22.1.0.tgz#2277605b40ed4529ae4db51ff62f4be817647914"
+  dependencies:
+    ansi-regex "^3.0.0"
+    ansi-styles "^3.2.0"
+
 private@^0.1.6, private@~0.1.5:
   version "0.1.7"
   resolved "https://registry.yarnpkg.com/private/-/private-0.1.7.tgz#68ce5e8a1ef0a23bb570cc28537b5332aba63ef1"