Add custom reporter to produce Problem Matcher output

jest.config.js

@@ -0,0 +1,3 @@
+module.exports = {
+    "reporters": ["<rootDir>/json-reporter.js"]
+}

json-reporter.js

@@ -0,0 +1,30 @@
+class MyCustomReporter {
+  constructor(globalConfig, options) {
+    this._globalConfig = globalConfig;
+    this._options = options;
+  }
+
+  onRunComplete(contexts, results) {
+    results.testResults[0].testResults.forEach((item) => {
+      if (item.status !== "failed") {
+        return;
+      }
+      const newLine = "%0A";
+      const name = results.testResults[0].testFilePath;
+
+      if (!item.location) {
+        throw new Error(
+          "You need to invoked jest with argument --testLocationInResults"
+        );
+      }
+
+      const line = item.location.line + 1;
+      const col = item.location.column;
+      const message = item.failureMessages[0].replace(/\n/g, newLine);
+
+      console.log(`::error file=${name},line=${line},col=${col}::${message}`);
+    });
+  }
+}
+
+module.exports = MyCustomReporter;

package.json

@@ -4,7 +4,7 @@
   "description": "",
   "main": "index.js",
   "scripts": {
-    "test": "jest ."
+    "test": "jest . --testLocationInResults"
   },
   "keywords": [],
   "author": "",

some.test.js

@@ -2,4 +2,8 @@ describe("foo", function() {
   it("passes", function() {
     expect("a").toBe("a");
   });
+
+  it("fails", function() {
+    expect("a").toBe("b");
+  });
 });