Add tests for chainFn

lib/common/utils.js

@@ -72,6 +72,7 @@ export function chainFn (base, fn) {
   if (!(fn instanceof Function)) {
     return
   }
+  return function () {
     if (typeof base !== 'function') {
       return fn.apply(this, arguments)
     }
@@ -80,12 +81,13 @@ export function chainFn (base, fn) {
     if (baseResult === undefined) {
       baseResult = arguments[0]
     }
-  let fnResult = fn.call(this, baseResult, ...arguments.slice(1))
+    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
+  }
 }
 
 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)
+})