Add testing for map subtract

lib/debuglet.js

@@ -254,13 +254,13 @@ Debuglet.prototype.updateActiveBreakpoints_ = function(breakpoints) {
   });
 
   // Remove completed breakpoints that the server no longer cares about.
-  mapSubtract(this.completedBreakpointMap_, updatedBreakpointMap)
+  Debuglet.mapSubtract(this.completedBreakpointMap_, updatedBreakpointMap)
     .forEach(function(breakpoint){
       delete this.completedBreakpointMap_[breakpoint.id];
     }, this);
 
   // Remove active breakpoints that the server no longer care about.
-  mapSubtract(this.activeBreakpointMap_, updatedBreakpointMap)
+  Debuglet.mapSubtract(this.activeBreakpointMap_, updatedBreakpointMap)
     .forEach(this.removeBreakpoint_, this);
 };
 
@@ -396,17 +396,16 @@ Debuglet.prototype.stop = function() {
 
 /**
  * Performs a set subtract. Returns A - B given maps A, B.
- * TODO(ofrobots): we need unit tests for this
  * @return {Array.<Breakpoint>} A array containing elements from A that are not
  *     in B.
  */
-function mapSubtract(A, B) {
+Debuglet.mapSubtract = function mapSubtract(A, B) {
   var removed = [];
   for (var key in A) {
     if (!B[key]) {
       removed.push(A[key]);
     }
   }
   return removed;
-}
+};
 

test/standalone/test-debuglet.js

@@ -247,5 +247,16 @@ describe(__filename, function(){
 
     debuglet.start();
   });
+
+  describe('map subtract', function() {
+    it('should be correct', function() {
+      var a = { a: 1, b: 2 };
+      var b = { a: 1 };
+      assert.deepEqual(Debuglet.mapSubtract(a, b), [2]);
+      assert.deepEqual(Debuglet.mapSubtract(b, a), []);
+      assert.deepEqual(Debuglet.mapSubtract(a, {}), [1, 2]);
+      assert.deepEqual(Debuglet.mapSubtract({}, b), []);
+    });
+  });
 });