test(plugin): add some utils for testing

package.json

@@ -42,7 +42,8 @@
     "parse5": "^6.0.0",
     "parse5-htmlparser2-tree-adapter": "^6.0.0",
     "purgecss": "^4.0.0",
-    "filesize": "^6.1.0"
+    "filesize": "^6.1.0",
+    "mkdirp": "^1.0.4"
   },
   "devDependencies": {
     "@babel/cli": "7.12.16",

test/__mocks__/fs.js

@@ -0,0 +1,5 @@
+import MemoryFS from 'metro-memory-fs'
+// Make sure we export this as a cjs module
+module.exports = new MemoryFS({
+  cwd: () => '/virtual/project'
+})

test/utils.js

@@ -0,0 +1,70 @@
+import fs from 'fs'
+import path from 'path'
+import mkdirp from 'mkdirp'
+import { onPreBootstrap } from '../src'
+
+/**
+ * Make sure to mock the fs module in your test
+ * file before using any of these functions
+ */
+
+/**
+ * Virtual project root directory
+ * @see /test/__mocks__/fs.js
+ * @type {string}
+ */
+export const programRoot = '/virtual/project'
+
+/**
+ * Changes plugin options by invoking the onPreBootstrap hook
+ * Tests that run after calling this function will receive
+ * the mounted options
+ *
+ * Note: Make sure to wrap this in a try..catch block when you
+ * pass custom options since it may throw errors
+ *
+ * @param {Object} options
+ */
+export function mountOptions (options = {}) {
+  onPreBootstrap({
+    store: {
+      getState: () => ({
+        program: { directory: programRoot }
+      })
+    },
+    reporter: {},
+    pathPrefix: ''
+  }, options)
+}
+
+/**
+ * Mounts a directory on the virtual filesystem
+ *
+ * @param {string} dirname
+ */
+export function mountDir (dirname) {
+  dirname = path.resolve(programRoot, dirname)
+  !fs.existsSync(dirname) ? mkdirp.sync(dirname) : null
+}
+
+/**
+ * Mounts a file on the virtual filesystem
+ *
+ * @param {string} filename
+ * @param {string} content
+ */
+export function mountFile (filename, content = '//noop') {
+  mountDir(path.dirname(filename))
+  fs.writeFileSync(path.resolve(programRoot, filename), content.toString())
+}
+
+/**
+ * Mocks a virtual module by path Usefull when requiring
+ * a module that doesn't exist on the filesystem
+ *
+ * @param {string} name - module name
+ * @param {object} exports - module exports
+ */
+export function mountModule (name, exports) {
+  jest.doMock(path.resolve(programRoot, name), () => exports, { virtual: true })
+}