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 +1,35 @@
+class MyCustomReporter {
+  constructor(globalConfig, options) {
+    this._globalConfig = globalConfig;
+    this._options = options;
+  }
+
+  onRunComplete(contexts, results) {
+    results.testResults.forEach((testResultItem) => {
+      const testFilePath = testResultItem.testFilePath;
+
+      testResultItem.testResults.forEach((result) => {
+          if (result.status !== "failed") {
+            return;
+          }
+
+          result.failureMessages.forEach(failureMessages => {
+            const newLine = "%0A";
+            const message = failureMessages.replace(/\n/g, newLine);
+            const captureGroup = message.match(/:([0-9]+):([0-9]+)/);
+
+            if (!captureGroup) {
+              console.log('Unable to extract line number from call stack')
+              return;
+            }
+
+            const [, line, col] = captureGroup;
+            console.log(`::error file=${testFilePath},line=${line},col=${col}::${message}`);
+          })
+
+        });
+    })
+  }
+}
+
+module.exports = MyCustomReporter;

some.test.js

@@ -2,4 +2,14 @@ describe("foo", function() {
   it("passes", function() {
     expect("a").toBe("a");
   });
+
+  it("fails", function() {
+    expect("b").toBe("b");
+    expect("c").toBe("d");
+    expect("d").toBe("c");
+  });
+
+  it("fails II", function() {
+    expect(1).toBe(2);
+  });
 });