feat: Add nyc-test-coverage package (#798)

* add working nyc-test-coverage package

* address a couple of comments

* avoid using global coverageMap

* address Roeys comments

* address code review comments, add README

* address Roey's comments and add some more details to the README

Author: vkarpov15

packages/nyc-test-coverage/README.md

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+# `@temporalio/nyc-test-coverage`
+
+[![NPM](https://img.shields.io/npm/v/@temporalio/nyc-test-coverage?style=for-the-badge)](https://www.npmjs.com/package/@temporalio/nyc-test-coverage)
+
+[Temporal](https://temporal.io)'s [TypeScript SDK](https://docs.temporal.io/typescript/introduction) interceptors and sinks for code coverage with [nyc](https://npmjs.com/package/nyc).
+
+## Getting Started
+
+1. `npm install mocha nyc`
+2. Use [nyc to manually instrument your Workflow code](https://github.com/istanbuljs/nyc/blob/master/docs/instrument.md), for example `nyc instrument lib lib --in-place`. Make sure you instrument your Workflow code _after_ compiling it with `tsc`.
+3. Add this package's sinks and interceptors to your test worker, for example:
+
+```ts
+import { WorkflowCoverage } from '@temporalio/nyc-test-coverage';
+
+const workflowCoverage = new WorkflowCoverage();
+
+worker = await Worker.create({
+  connection: nativeConnection,
+  taskQueue,
+  workflowsPath: require.resolve("./workflows"),
+  interceptors: {
+    workflowModules: [require.resolve("@temporalio/nyc-test-coverage/lib/interceptors")]
+  },
+  sinks: workflowCoverage.sinks,
+});
+```
+
+4. After your tests are done, call `mergeIntoGlobalCoverage()` to merge your Workflows' code coverage into nyc's global coverage.
+
+```ts
+after(() => {
+  workflowCoverage.mergeIntoGlobalCoverage();
+});
+```
+
+For example, the following is a sample npm script that handles instrumenting and running tests.
+The following assumes that `npm run build` produces compiled JavaScript in the `lib` directory.
+
+```
+{
+  "test.coverage": "npm run build && nyc instrument lib lib --in-place && nyc --reporter=lcov --reporter=text-summary mocha lib/*.test.js"
+}
+```

packages/nyc-test-coverage/package.json

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+{
+  "name": "@temporalio/nyc-test-coverage",
+  "version": "1.0.1",
+  "description": "Temporal.io SDK code coverage integration",
+  "main": "lib/index.js",
+  "types": "./lib/index.d.ts",
+  "keywords": [
+    "temporal",
+    "workflow",
+    "testing",
+    "coverage"
+  ],
+  "author": "Temporal Technologies Inc. <sdk@temporal.io>",
+  "license": "MIT",
+  "dependencies": {
+    "@temporalio/workflow": "file:../workflow",
+    "@temporalio/worker": "file:../worker",
+    "istanbul-lib-coverage": "^3.2.0"
+  },
+  "devDependencies": {
+    "@types/istanbul-lib-coverage": "^2.0.4"
+  },
+  "bugs": {
+    "url": "https://github.com/temporalio/sdk-typescript/issues"
+  },
+  "homepage": "https://github.com/temporalio/sdk-typescript/tree/main/packages/testing",
+  "files": [
+    "lib",
+    "src"
+  ],
+  "publishConfig": {
+    "access": "public"
+  }
+}

packages/nyc-test-coverage/src/index.ts

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+import { InjectedSinks } from '@temporalio/worker';
+import { CoverageSinks } from './sinks';
+import libCoverage from 'istanbul-lib-coverage';
+
+export class WorkflowCoverage {
+  coverageMap = libCoverage.createCoverageMap();
+
+  /**
+   * Contains sinks that allow Workflows to gather coverage data.
+   */
+  get sinks(): InjectedSinks<CoverageSinks> {
+    return {
+      coverage: {
+        merge: {
+          fn: (_workflowInfo, testCoverage) => {
+            this.coverageMap.merge(testCoverage);
+          },
+          callDuringReplay: false,
+        },
+      },
+    };
+  }
+
+  /**
+   * Merge this WorkflowCoverage's coverage map into the global coverage
+   * map data `global.__coverage__`.
+   */
+  mergeIntoGlobalCoverage(): void {
+    /* eslint-disable @typescript-eslint/ban-ts-comment */
+    // @ts-ignore
+    this.coverageMap.merge(global.__coverage__);
+
+    const coverageMapData: libCoverage.CoverageMapData = Object.keys(this.coverageMap.data).reduce(
+      (cur: libCoverage.CoverageMapData, path) => {
+        const fileCoverage = this.coverageMap.data[path] as libCoverage.FileCoverage;
+
+        cur[path] = fileCoverage.data;
+        return cur;
+      },
+      {}
+    );
+
+    // @ts-ignore
+    global.__coverage__ = coverageMapData;
+  }
+}

packages/nyc-test-coverage/src/interceptors.ts

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+import { proxySinks, WorkflowInterceptors } from '@temporalio/workflow';
+import { CoverageSinks } from './sinks';
+import libCoverage from 'istanbul-lib-coverage';
+
+const { coverage } = proxySinks<CoverageSinks>();
+
+// Export the interceptors
+export const interceptors = (): WorkflowInterceptors => ({
+  internals: [
+    {
+      concludeActivation(input, next) {
+        /* eslint-disable @typescript-eslint/ban-ts-comment */
+        // @ts-ignore
+        const globalCoverage: libCoverage.CoverageMapData = global.__coverage__;
+
+        coverage.merge(JSON.parse(JSON.stringify(globalCoverage)));
+        clearCoverage(globalCoverage);
+
+        return next(input);
+      },
+    },
+  ],
+});
+
+function clearCoverage(coverage: libCoverage.CoverageMapData): void {
+  for (const path of Object.keys(coverage)) {
+    for (const index of Object.keys(coverage[path].s)) {
+      coverage[path].s[index] = 0;
+    }
+  }
+}

packages/nyc-test-coverage/src/sinks.ts

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+import { Sinks } from '@temporalio/workflow';
+
+export interface CoverageSinks extends Sinks {
+  coverage: {
+    merge(coverageMap: any): void;
+  };
+}

packages/nyc-test-coverage/tsconfig.json

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+{
+  "extends": "../../tsconfig.base.json",
+  "compilerOptions": {
+    "outDir": "./lib",
+    "rootDir": "./src"
+  },
+  "references": [{ "path": "../worker" }, { "path": "../workflow" }],
+  "include": ["./src/**/*.ts"]
+}