Add tests for chainFn

lib/common/utils.js

@@ -72,20 +72,22 @@ export function chainFn (base, fn) {
   if (!(fn instanceof Function)) {
     return
   }
-  if (typeof base !== 'function') {
-    return fn.apply(this, arguments)
+  return function () {
+    if (typeof base !== 'function') {
+      return fn.apply(this, arguments)
+    }
+    let baseResult = base.apply(this, arguments)
+    // Allow function to mutate the first argument instead of returning the result
+    if (baseResult === undefined) {
+      baseResult = arguments[0]
+    }
+    let fnResult = fn.call(this, baseResult, ...Array.prototype.slice.call(arguments, 1))
+    // Return mutated argument if no result was returned
+    if (fnResult === undefined) {
+      return baseResult
+    }
+    return fnResult
   }
-  let baseResult = base.apply(this, arguments)
-  // Allow function to mutate the first argument instead of returning the result
-  if (baseResult === undefined) {
-    baseResult = arguments[0]
-  }
-  let fnResult = fn.call(this, baseResult, ...arguments.slice(1))
-  // Return mutated argument if no result was returned
-  if (fnResult === undefined) {
-    return baseResult
-  }
-  return fnResult
 }
 
 export function isPureObject (o) {

test/utils.test.js

@@ -94,3 +94,52 @@ test('promisifyRoute (fn(cb) with result)', t => {
       t.is(res, array)
     })
 })
+
+test('chainFn (mutate, mutate)', t => {
+  // Pass more than one argument to test that they're actually taken into account
+  const firstFn = function (obj, count) {
+    obj.foo = count + 1
+  }
+  const secondFn = function (obj, count) {
+    obj.bar = count + 2
+  }
+  const chainedFn = Utils.chainFn(firstFn, secondFn)
+  const expectedResult = { foo: 11, bar: 12 }
+  t.deepEqual(chainedFn({}, 10), expectedResult)
+})
+
+test('chainFn (mutate, return)', t => {
+  const firstFn = function (obj, count) {
+    obj.foo = count + 1
+  }
+  const secondFn = function (obj, count) {
+    return Object.assign({}, obj, { bar: count + 2 })
+  }
+  const chainedFn = Utils.chainFn(firstFn, secondFn)
+  const expectedResult = { foo: 11, bar: 12 }
+  t.deepEqual(chainedFn({}, 10), expectedResult)
+})
+
+test('chainFn (return, mutate)', t => {
+  const firstFn = function (obj, count) {
+    return Object.assign({}, obj, { foo: count + 1 })
+  }
+  const secondFn = function (obj, count) {
+    obj.bar = count + 2
+  }
+  const chainedFn = Utils.chainFn(firstFn, secondFn)
+  const expectedResult = { foo: 11, bar: 12 }
+  t.deepEqual(chainedFn({}, 10), expectedResult)
+})
+
+test('chainFn (return, return)', t => {
+  const firstFn = function (obj, count) {
+    return Object.assign({}, obj, { foo: count + 1 })
+  }
+  const secondFn = function (obj, count) {
+    return Object.assign({}, obj, { bar: count + 2 })
+  }
+  const chainedFn = Utils.chainFn(firstFn, secondFn)
+  const expectedResult = { foo: 11, bar: 12 }
+  t.deepEqual(chainedFn({}, 10), expectedResult)
+})