Merge pull request #621 from lucasfcosta/change-by-delta

[WIP] Change by delta (New Assertion)
chaijs · Feb 23, 2016 · a97b22f · a97b22f
2 parents a9b0706 + 10a0bbc
commit a97b22f
Show file tree

Hide file tree

Showing 5 changed files with 383 additions and 45 deletions.
diff --git a/lib/chai/core/assertions.js b/lib/chai/core/assertions.js
@@ -42,7 +42,7 @@ module.exports = function (chai, _) {
   [ 'to', 'be', 'been'
   , 'is', 'and', 'has', 'have'
   , 'with', 'that', 'which', 'at'
-  , 'of', 'same' ].forEach(function (chain) {
+  , 'of', 'same', 'but' ].forEach(function (chain) {
     Assertion.addProperty(chain, function () {
       return this;
     });
@@ -1634,31 +1634,38 @@ module.exports = function (chai, _) {
    * @name change
    * @alias changes
    * @alias Change
-   * @param {String} object
+   * @param {String} target
    * @param {String} property name _optional_
    * @param {String} message _optional_
    * @namespace BDD
    * @api public
    */
 
-  function assertChanges (object, prop, msg) {
+  function assertChanges (target, prop, msg) {
     if (msg) flag(this, 'message', msg);
     var fn = flag(this, 'object');
     new Assertion(fn).is.a('function');
 
     var initial;
     if (!prop) {
-      new Assertion(object).is.a('function');
-      initial = object();
+      new Assertion(target).is.a('function');
+      initial = target();
     } else {
-      new Assertion(object, msg).to.have.property(prop);
-      initial = object[prop];
+      new Assertion(target, msg).to.have.property(prop);
+      initial = target[prop];
     }
 
     fn();
 
-    var final = prop === undefined ? object() : object[prop];
-    var msgObj = prop === undefined ? initial : '.' + prop;
+    var final = prop === undefined || prop === null ? target() : target[prop];
+    var msgObj = prop === undefined || prop === null ? initial : '.' + prop;
+
+    // This gets flagged because of the .by(delta) assertion
+    flag(this, 'deltaMsgObj', msgObj);
+    flag(this, 'initialDeltaValue', initial);
+    flag(this, 'finalDeltaValue', final);
+    flag(this, 'deltaBehavior', 'change');
+    flag(this, 'realDelta', final !== initial);
 
     this.assert(
       initial !== final
@@ -1682,31 +1689,37 @@ module.exports = function (chai, _) {
    * @name increase
    * @alias increases
    * @alias Increase
-   * @param {String} object
+   * @param {String} target
    * @param {String} property name
    * @param {String} message _optional_
    * @namespace BDD
    * @api public
    */
 
-  function assertIncreases (object, prop, msg) {
+  function assertIncreases (target, prop, msg) {
     if (msg) flag(this, 'message', msg);
     var fn = flag(this, 'object');
     new Assertion(fn).is.a('function');
 
     var initial;
     if (!prop) {
-      new Assertion(object).is.a('function');
-      initial = object();
+      new Assertion(target).is.a('function');
+      initial = target();
     } else {
-      new Assertion(object, msg).to.have.property(prop);
-      initial = object[prop];
+      new Assertion(target, msg).to.have.property(prop);
+      initial = target[prop];
     }
 
     fn();
 
-    var final = prop === undefined ? object() : object[prop];
-    var msgObj = prop === undefined ? initial : '.' + prop;
+    var final = prop === undefined || prop === null ? target() : target[prop];
+    var msgObj = prop === undefined || prop === null ? initial : '.' + prop;
+
+    flag(this, 'deltaMsgObj', msgObj);
+    flag(this, 'initialDeltaValue', initial);
+    flag(this, 'finalDeltaValue', final);
+    flag(this, 'deltaBehavior', 'increase');
+    flag(this, 'realDelta', final - initial);
 
     this.assert(
       final - initial > 0
@@ -1730,31 +1743,37 @@ module.exports = function (chai, _) {
    * @name decrease
    * @alias decreases
    * @alias Decrease
-   * @param {String} object
+   * @param {String} target
    * @param {String} property name
    * @param {String} message _optional_
    * @namespace BDD
    * @api public
    */
 
-  function assertDecreases (object, prop, msg) {
+  function assertDecreases (target, prop, msg) {
     if (msg) flag(this, 'message', msg);
     var fn = flag(this, 'object');
     new Assertion(fn).is.a('function');
 
     var initial;
     if (!prop) {
-      new Assertion(object).is.a('function');
-      initial = object();
+      new Assertion(target).is.a('function');
+      initial = target();
     } else {
-      new Assertion(object, msg).to.have.property(prop);
-      initial = object[prop];
+      new Assertion(target, msg).to.have.property(prop);
+      initial = target[prop];
     }
 
     fn();
 
-    var final = prop === undefined ? object() : object[prop];
-    var msgObj = prop === undefined ? initial : '.' + prop;
+    var final = prop === undefined || prop === null ? target() : target[prop];
+    var msgObj = prop === undefined || prop === null ? initial : '.' + prop;
+
+    flag(this, 'deltaMsgObj', msgObj);
+    flag(this, 'initialDeltaValue', initial);
+    flag(this, 'finalDeltaValue', final);
+    flag(this, 'deltaBehavior', 'decrease');
+    flag(this, 'realDelta', initial - final);
 
     this.assert(
       final - initial < 0
@@ -1766,6 +1785,45 @@ module.exports = function (chai, _) {
   Assertion.addChainableMethod('decrease', assertDecreases);
   Assertion.addChainableMethod('decreases', assertDecreases);
 
+  /**
+   * ### .by
+   *
+   * Defines an amount for increase/decrease assertions.
+   *
+   *     var obj = { val: 10 };
+   *     var dec = function() { obj.val -= 5 };
+   *     var inc = function() {obj.val += 10};
+   *     expect(dec).to.decrease(obj, 'val').by(5);
+   *     expect(inc).to.increase(obj, 'val').by(10);
+   *
+   * @name by
+   * @namespace BDD
+   * @api public
+   */
+
+  function assertDelta(delta) {
+    var msgObj = flag(this, 'deltaMsgObj');
+    var initial = flag(this, 'initialDeltaValue');
+    var final = flag(this, 'finalDeltaValue');
+    var behavior = flag(this, 'deltaBehavior');
+    var realDelta = flag(this, 'realDelta');
+
+    var expression;
+    if (behavior === 'change') {  
+      expression = Math.abs(final - initial) === Math.abs(delta);
+    } else {
+      expression = realDelta === Math.abs(delta);
+    }
+
+    this.assert(
+      expression
+      , 'expected ' + msgObj + ' to ' + behavior + ' by ' + delta
+      , 'expected ' + msgObj + ' to not ' + behavior + ' by ' + delta
+    );
+  }
+
+  Assertion.addMethod('by', assertDelta);
+
   /**
    * ### .extensible
    *