Add possibility to create coverage reports (#9029)

.eslintrc.js

@@ -9,6 +9,7 @@ module.exports = {
 		'docs/examples/extending/extending-2-layers.md',
 		'docs/_posts/201*',
 		'docs/_site',
+		'coverage'
 	],
 	root: true,
 	globals: {

package.json

@@ -12,9 +12,11 @@
     "eslint-plugin-import": "^2.27.5",
     "http-server": "^14.1.1",
     "husky": "^8.0.1",
+    "istanbul": "^0.4.5",
     "karma": "^6.4.1",
     "karma-chai": "^0.1.0",
     "karma-chrome-launcher": "^3.1.1",
+    "karma-coverage": "^2.2.1",
     "karma-firefox-launcher": "^2.1.2",
     "karma-mocha": "^2.0.1",
     "karma-safarinative-launcher": "^1.1.0",
@@ -46,6 +48,7 @@
     "debug": "http-server -c-1",
     "docs": "node ./build/docs.mjs && node ./build/integrity.mjs",
     "test": "karma start ./spec/karma.conf.js",
+    "coverage": "karma start ./spec/karma.conf.js --coverage --single-run",
     "build": "npm run rollup && npm run uglify",
     "lint": "eslint . --ext js,mjs,cjs",
     "lintfix": "npm run lint -- --fix",

spec/karma.conf.js

@@ -1,6 +1,9 @@
+/* eslint-env node */
 // See: https://karma-runner.github.io/latest/config/configuration-file.html
 module.exports = function (/** @type {import('karma').Config} */ config) {
-	config.set({
+	const isCoverageEnabled = process.argv.includes('--coverage');
+
+	const karmaConfig = {
 		basePath: '../',
 		plugins: [
 			'karma-mocha',
@@ -24,6 +27,13 @@ module.exports = function (/** @type {import('karma').Config} */ config) {
 			{pattern: 'dist/*.css', type: 'css'},
 		],
 		reporters: ['progress', 'time-stats'],
+		coverageReporter: {
+			dir: 'coverage/',
+			reporters: [
+				{type: 'html', subdir: 'html'},
+				{type: 'text-summary'}
+			]
+		},
 		timeStatsReporter: {
 			reportTimeStats: false,
 			longestTestsCount: 10
@@ -64,5 +74,15 @@ module.exports = function (/** @type {import('karma').Config} */ config) {
 				forbidOnly: process.env.CI || false
 			}
 		}
-	});
+	};
+
+	if (isCoverageEnabled) {
+		karmaConfig.plugins.push('karma-coverage');
+		karmaConfig.reporters.push('coverage');
+		karmaConfig.preprocessors = {
+			'dist/leaflet-src.esm.js': 'coverage'
+		};
+	}
+
+	config.set(karmaConfig);
 };