Restore commands after each spec

This commit adds the ability to get and restore snapshots of command
listeners. Whatever commands are installed before specs begin are
preserved, but commands added during specs are always cleared away.

spec/command-registry-spec.coffee

@@ -145,3 +145,31 @@ describe "CommandRegistry", ->
       expect(registry.dispatch(grandchild, 'command')).toBe true
       expect(registry.dispatch(grandchild, 'bogus')).toBe false
       expect(registry.dispatch(parent, 'command')).toBe false
+
+  describe "::getSnapshot and ::restoreSnapshot", ->
+    it "removes all command handlers except for those in the snapshot", ->
+      registry.add '.parent', 'namespace:command-1', ->
+      registry.add '.child', 'namespace:command-2', ->
+      snapshot = registry.getSnapshot()
+      registry.add '.grandchild', 'namespace:command-3', ->
+
+      expect(registry.findCommands(target: grandchild)[0..2]).toEqual [
+        {name: 'namespace:command-3', displayName: 'Namespace: Command 3'}
+        {name: 'namespace:command-2', displayName: 'Namespace: Command 2'}
+        {name: 'namespace:command-1', displayName: 'Namespace: Command 1'}
+      ]
+
+      registry.restoreSnapshot(snapshot)
+
+      expect(registry.findCommands(target: grandchild)[0..1]).toEqual [
+        {name: 'namespace:command-2', displayName: 'Namespace: Command 2'}
+        {name: 'namespace:command-1', displayName: 'Namespace: Command 1'}
+      ]
+
+      registry.add '.grandchild', 'namespace:command-3', ->
+      registry.restoreSnapshot(snapshot)
+
+      expect(registry.findCommands(target: grandchild)[0..1]).toEqual [
+        {name: 'namespace:command-2', displayName: 'Namespace: Command 2'}
+        {name: 'namespace:command-1', displayName: 'Namespace: Command 1'}
+      ]

spec/spec-helper.coffee

@@ -27,6 +27,7 @@ fixturePackagesPath = path.resolve(__dirname, './fixtures/packages')
 atom.packages.packageDirPaths.unshift(fixturePackagesPath)
 atom.keymaps.loadBundledKeymaps()
 keyBindingsToRestore = atom.keymaps.getKeyBindings()
+commandsToRestore = atom.commands.getSnapshot()
 
 $(window).on 'core:close', -> window.close()
 $(window).on 'beforeunload', ->
@@ -65,6 +66,7 @@ beforeEach ->
   atom.workspace = new Workspace()
   atom.keymaps.keyBindings = _.clone(keyBindingsToRestore)
   atom.commands.setRootNode(document.body)
+  atom.commands.restoreSnapshot(commandsToRestore)
 
   window.resetTimeouts()
   atom.packages.packageStates = {}

src/command-registry.coffee

@@ -46,6 +46,8 @@ class CommandRegistry
   constructor: (@rootNode) ->
     @listenersByCommandName = {}
 
+  getRootNode: -> @rootNode
+
   setRootNode: (newRootNode) ->
     oldRootNode = @rootNode
     @rootNode = newRootNode
@@ -149,6 +151,15 @@ class CommandRegistry
     eventWithTarget = Object.create(event, target: value: target)
     @handleCommandEvent(eventWithTarget)
 
+  getSnapshot: ->
+    _.deepClone(@listenersByCommandName)
+
+  restoreSnapshot: (snapshot) ->
+    rootNode = @getRootNode()
+    @setRootNode(null) # clear listeners for current commands
+    @listenersByCommandName = _.deepClone(snapshot)
+    @setRootNode(rootNode) # restore listeners for commands in snapshot
+
   handleCommandEvent: (event) =>
     propagationStopped = false
     immediatePropagationStopped = false