Extend callbackToPromise tests

- Add 100% coverage
- Test promise reject
- Test callbackArgIndex argument usage

lib/callback_to_promise.js

@@ -1,4 +1,3 @@
-// istanbul ignore file
 'use strict';
 
 var Promise = require('./promise');

test/callback_to_promise.test.js

@@ -7,6 +7,10 @@ describe('callbackToPromise', function() {
         callback(null, this + value);
     }
 
+    function rejectValue(value, callback) {
+        callback(new Error('I reject this value'));
+    }
+
     function sum() {
         var callback = arguments[arguments.length - 1];
         var result = 0;
@@ -16,11 +20,16 @@ describe('callbackToPromise', function() {
         callback(null, result);
     }
 
-    it('lets a function return a promise', function() {
+    it('lets a function return a promise that can resolve', function() {
         var wrapped = callbackToPromise(returnThisPlusValue, 1);
         expect(wrapped(2)).resolves.toBe(3);
     });
 
+    it('lets a function return a promise that can reject', function() {
+        var wrapped = callbackToPromise(rejectValue, 1);
+        expect(wrapped(2)).rejects.toThrow(/reject this value/);
+    });
+
     it('maintains the ability to call a function with a callback', function(done) {
         var wrapped = callbackToPromise(returnThisPlusValue, 1);
         wrapped(2, function(err, result) {
@@ -47,4 +56,9 @@ describe('callbackToPromise', function() {
             });
         });
     });
+
+    it('can allow the user to explicately identify the index of the callback', function() {
+        var wrapped = callbackToPromise(returnThisPlusValue, 1, 1);
+        expect(wrapped(2)).resolves.toBe(3);
+    });
 });