Allow us to write Jest tests!

Change-Id: I6095b08dd72a7ba0ac6bd13c5f5870a1e23c7748

.gitignore

@@ -1,3 +1,4 @@
+/coverage/
 /docs/
 /node_modules/
 /vendor

jest.config.js

@@ -0,0 +1,61 @@
+'use strict';
+
+// For a detailed explanation regarding each configuration property, visit:
+// https://jestjs.io/docs/en/configuration.html
+
+module.exports = {
+	moduleNameMapper: {
+	},
+
+	// Automatically clear mock calls and instances between every test
+	clearMocks: true,
+
+	// Indicates whether the coverage information should be collected while executing the test
+	collectCoverage: true,
+
+	// An array of glob patterns indicating a set of files fo
+	//  which coverage information should be collected
+	collectCoverageFrom: [
+		'resources/**/*.(js|vue)'
+	],
+
+	// The directory where Jest should output its coverage files
+	coverageDirectory: 'coverage',
+
+	// An array of regexp pattern strings used to skip coverage collection
+	coveragePathIgnorePatterns: [
+		'/node_modules/'
+	],
+
+	// An object that configures minimum threshold enforcement for coverage results
+	coverageThreshold: {
+		global: {
+			branches: 0,
+			functions: 0,
+			lines: 0,
+			statements: 0
+		}
+	},
+
+	// An array of file extensions your modules use
+	moduleFileExtensions: [
+		'js',
+		'json',
+		'vue'
+	],
+
+	modulePathIgnorePatterns: [
+		'<rootDir>/tests/qunit/'
+	],
+
+	// The paths to modules that run some code to configure or
+	// set up the testing environment before each test
+	setupFiles: [
+		'./jest.setup.js'
+	],
+
+	testEnvironment: 'jsdom',
+
+	transform: {
+	}
+};

jest.setup.js

@@ -0,0 +1,2 @@
+'use strict';
+// In future we may want to define mw, or other globals here.

package.json

@@ -7,7 +7,8 @@
 		"lint:js": "eslint --cache .",
 		"lint:styles": "stylelint --cache --report-needless-disables **/*.{css,less}",
 		"lint:i18n": "banana-checker --requireLowerCase=0 i18n/",
-		"test": "npm run lint && npm run doc && dev-scripts/svg_check.sh",
+		"test": "npm run lint && npm run doc && dev-scripts/svg_check.sh && npm run test:unit",
+		"test:unit": "jest --silent --passWithNoTests",
 		"minify:svg": "svgo --config=.svgo.config.js --quiet --recursive --folder resources/",
 		"doc": "jsdoc -c jsdoc.json",
 		"selenium-test-cucumber": "wdio tests/selenium/wdio.conf.cucumber.js",
@@ -30,5 +31,8 @@
 		"stylelint-config-wikimedia": "0.16.1",
 		"svgo": "3.2.0",
 		"wdio-mediawiki": "2.5.0"
+	},
+	"dependencies": {
+		"jest": "^27.4.7"
 	}
 }