try Stryker (v2) testing, for evaluation, etc. - outdated

.gitignore

@@ -17,3 +17,5 @@
 coverage
 .idea
 package-lock.json
+.stryker-tmp
+reports

package.json

@@ -78,6 +78,9 @@
     "@babel/preset-env": "7.7.1",
     "@rollup/plugin-alias": "2.2.0",
     "@rollup/plugin-replace": "2.2.1",
+    "@stryker-mutator/core": "2.3.0",
+    "@stryker-mutator/html-reporter": "2.3.0",
+    "@stryker-mutator/javascript-mutator": "2.3.0",
     "babel-loader": "8.0.6",
     "benchmark": "2.1.4",
     "builtin-modules": "3.1.0",
@@ -127,6 +130,7 @@
     "lint": "cross-env EFF_NO_LINK_RULES=true eslint . --format friendly",
     "lint-docs": "prettylint {.,docs,website,website/blog}/*.md",
     "lint-dist": "eslint --no-eslintrc --no-ignore --env=browser \"dist/!(bin-prettier|index|third-party).js\"",
+    "stryker": "stryker run",
     "build": "node --max-old-space-size=3072 ./scripts/build/build.js",
     "build-docs": "node ./scripts/build-docs.js",
     "check-deps": "node ./scripts/check-deps.js",

stryker.conf.js

@@ -0,0 +1,26 @@
+"use strict";
+
+module.exports = function(config) {
+  config.set({
+    mutator: "javascript",
+    mutate: [
+      // [FUTURE TBD] this seems to take about 100 hours on a 40-CPU server in the cloud:
+      // "src/**/*.js"
+      // [TBD] mutation testing limited to src/common for now:
+      // "src/cli/*.js"
+      // ... , ...
+      "src/common/*.js"
+      // ... , ...
+      // "src/language-js/*.js"
+      // ... , ...
+      // "src/utils/*.js"
+    ],
+    packageManager: "yarn",
+    reporters: ["html", "clear-text", "progress"],
+    testRunner: "command",
+    // TBD ???:
+    timeoutMS: 15 * 60 * 1000,
+    transpilers: [],
+    coverageAnalysis: "off"
+  });
+};