Report on test coverage

src/cli/test/reporters/coverage.ts

@@ -0,0 +1,79 @@
+import type { AggregatedResult } from '@jest/test-result';
+import istanbulReport from 'istanbul-lib-report';
+import istanbulReports from 'istanbul-reports';
+
+export const createWriteOverride = () => {
+  const chunks: Uint8Array[] = [];
+
+  const output = () => Buffer.concat(chunks).toString('utf8');
+
+  const write = (
+    buffer: Uint8Array | string,
+    encodingOrCb?: BufferEncoding | ((err?: Error) => void),
+    cb?: (err?: Error) => void,
+  ) => {
+    chunks.push(
+      typeof buffer === 'string'
+        ? Buffer.from(
+            buffer,
+            typeof encodingOrCb === 'string' ? encodingOrCb : undefined,
+          )
+        : buffer,
+    );
+
+    if (typeof encodingOrCb === 'function') {
+      encodingOrCb();
+    } else {
+      cb?.();
+    }
+
+    return true;
+  };
+
+  return {
+    output,
+    write,
+  };
+};
+
+/**
+ * Renders out test coverage using the Istanbul `text` reporter.
+ *
+ * This is unfortunately hacky in a couple of ways;
+ *
+ * 1. Jest does not support custom coverage reporters (facebook/jest#9112), so
+ *    we rely on the default `CoverageReporter` running before us and use the
+ *   `coverageMap` that it places on the aggregated result state.
+ *
+ * 2. `istanbul-reports` does not support writing to a custom stream, so we need
+ *    to temporarily override `process.stdout.write` 😱.
+ *
+ * {@link https://github.com/facebook/jest/blob/v27.3.1/packages/jest-reporters/src/CoverageReporter.ts#L103}
+    //
+ */
+export const renderCoverageText = (
+  coverageMap: AggregatedResult['coverageMap'],
+) => {
+  if (!coverageMap) {
+    // Coverage was not stored on the aggregated result by `CoverageReporter`.
+    // Maybe `collectCoverage` / `--coverage` was not specified.
+    return;
+  }
+
+  const reportContext = istanbulReport.createContext({
+    coverageMap,
+  });
+
+  const overrideWrite = createWriteOverride();
+
+  const originalWrite = process.stdout.write.bind(this);
+  process.stdout.write = overrideWrite.write;
+
+  try {
+    istanbulReports.create('text').execute(reportContext);
+  } finally {
+    process.stdout.write = originalWrite;
+  }
+
+  return overrideWrite.output();
+};

src/cli/test/reporters/github/index.ts

@@ -2,21 +2,24 @@ import { inspect } from 'util';
 
 import type { Reporter, TestContext } from '@jest/reporters';
 import type { AggregatedResult } from '@jest/test-result';
+import stripAnsi from 'strip-ansi';
 
+import * as Buildkite from '../../../../api/buildkite';
 import * as GitHub from '../../../../api/github';
 import {
   buildNameFromEnvironment,
   enabledFromEnvironment,
 } from '../../../../api/github/environment';
 import { log } from '../../../../utils/logging';
 import { throwOnTimeout } from '../../../../utils/wait';
+import { renderCoverageText } from '../coverage';
 
 import { generateAnnotationEntries } from './annotations';
 
 export default class GitHubReporter implements Pick<Reporter, 'onRunComplete'> {
   async onRunComplete(
     _contexts: Set<TestContext>,
-    { testResults }: AggregatedResult,
+    { coverageMap, testResults }: AggregatedResult,
   ): Promise<void> {
     if (!enabledFromEnvironment()) {
       return;
@@ -27,6 +30,8 @@ export default class GitHubReporter implements Pick<Reporter, 'onRunComplete'> {
     let lastCheckRun: CheckRun | undefined;
 
     try {
+      const coverage = renderCoverageText(coverageMap);
+
       const entries = generateAnnotationEntries(testResults);
 
       const build = buildNameFromEnvironment();
@@ -47,6 +52,9 @@ export default class GitHubReporter implements Pick<Reporter, 'onRunComplete'> {
           annotations,
           conclusion: isOk ? 'success' : 'failure',
           summary,
+          text: coverage
+            ? Buildkite.md.terminal(stripAnsi(coverage))
+            : undefined,
           title: `${build} ${isOk ? 'passed' : 'failed'}`,
         };