add cache system

lib/mock.js

@@ -1,6 +1,25 @@
 const Module = require('module')
 
+const getKey = (a, b, c) =>
+  `${a}${b}${
+    JSON.stringify(c, (_, val) => typeof val !== 'object' ? String(val) : val)
+  }`
+
 class Mock {
+  static cache () {
+    if (!this._cache)
+      this._cache = new Map()
+    return this._cache
+  }
+
+  static setToCache({ parentFilename, filename, mocks, module }) {
+    this.cache().set(getKey(parentFilename, filename, mocks), module)
+  }
+
+  static getFromCache({ parentFilename, filename, mocks }) {
+    return this.cache().get(getKey(parentFilename, filename, mocks))
+  }
+
   constructor(parentFilename, filename, mocks = {}) {
     this.filename = filename
     this.mocks = new Map()
@@ -18,6 +37,12 @@ class Mock {
 are the same used in ${filename} require calls`)
     }
 
+    const cached = Mock.getFromCache({ parentFilename, filename, mocks })
+    if (cached) {
+      this.module = cached
+      return
+    }
+
     const self = this
     const callerTestRef = Module._cache[parentFilename]
     const filePath = Module._resolveFilename(filename, callerTestRef)
@@ -48,6 +73,7 @@ are the same used in ${filename} require calls`)
 
     this.module = new MockedModule(filePath, callerTestRef)
     this.module.load(filePath)
+    Mock.setToCache({ parentFilename, filename, mocks, module: this.module })
   }
 
   static get(parentFilename, filename, mocks) {