Run coverage at the end of jest and configure thresholds (#8371)

* Run coverage at the end of jest and configure thresholds

* Better configure coverage sources and remoce ratchet

* Default to no coverage, with a command to run with coverage

jest.config.js

@@ -7,8 +7,9 @@ const reGatsby = /gatsby$/
 const gatsbyDir = pkgs.find(p => reGatsby.exec(p))
 const gatsbyBuildDirs = [`dist`].map(dir => path.join(gatsbyDir, dir))
 const builtTestsDirs = pkgs.map(p => path.join(p, `__tests__`))
-
-const ignoreDirs = [].concat(gatsbyBuildDirs, builtTestsDirs)
+const distDirs = pkgs.map(p => path.join(p, `dist`))
+const ignoreDirs = [].concat(gatsbyBuildDirs, builtTestsDirs, distDirs)
+const coverageDirs = pkgs.map(p => path.join(p, `src/**/*.js`))
 
 module.exports = {
   notify: true,
@@ -27,4 +28,15 @@ module.exports = {
   moduleNameMapper: {
     "^highlight.js$": `<rootDir>/node_modules/highlight.js/lib/index.js`,
   },
+  collectCoverage: false,
+  coverageReporters: [`json-summary`, `text`, `html`],
+  coverageThreshold: {
+    global: {
+      lines: 42,
+      statements: 43,
+      functions: 40,
+      branches: 42,
+    },
+  },
+  collectCoverageFrom: coverageDirs,
 }

package.json

@@ -70,10 +70,10 @@
     "publish-canary": "lerna publish --canary --yes",
     "publish-next": "lerna publish --npm-tag=next --bump=prerelease",
     "test": "npm-run-all -s lint jest",
+    "test:coverage": "jest --coverage",
     "test:update": "jest --updateSnapshot",
     "test:watch": "jest --watch",
     "test:integration": "jest --config=jest.integration.js",
-    "test_bkup": "npm-run-all -s lint test-node test-integration",
     "version": "prettier --write \"**/CHANGELOG.md\" --no-semi",
     "watch": "lerna run watch --no-sort --stream --concurrency 999"
   },