Destroy any existing pending pane item when adding a pending item

spec/pane-spec.coffee

@@ -132,6 +132,16 @@ describe "Pane", ->
       expect(-> pane.addItem('foo')).toThrow()
       expect(-> pane.addItem(1)).toThrow()
 
+    it "destroys any existing pending item if the new item is pending", ->
+      pane = new Pane(paneParams(items: []))
+      itemA = new Item("A")
+      itemB = new Item("B")
+      itemA.pending = true
+      itemB.pending = true
+      pane.addItem(itemA)
+      pane.addItem(itemB)
+      expect(itemA.isDestroyed()).toBe true
+
   describe "::activateItem(item)", ->
     pane = null
 
@@ -155,7 +165,7 @@ describe "Pane", ->
       pane.activateItem(pane.itemAtIndex(1))
       expect(observed).toEqual [pane.itemAtIndex(1)]
 
-    describe "activating pending items", ->
+    describe "when the item being activated is pending", ->
       itemC = null
       itemD = null
 
@@ -164,24 +174,18 @@ describe "Pane", ->
         itemD = new Item("D")
         itemC.pending = true
         itemD.pending = true
+
+      it "replaces the active item if it is pending", ->
         pane.activateItem(itemC)
-
-      it "opens pending item", ->
-        expect(pane.getItems().length).toBe 3
-        expect(pane.getActiveItem()).toBe pane.itemAtIndex(1)
-
-      it "replaces original pending item when activating another pending item", ->
+        expect(pane.getItems().map (item) -> item.name).toEqual ['A', 'C', 'B']
         pane.activateItem(itemD)
+        expect(pane.getItems().map (item) -> item.name).toEqual ['A', 'D', 'B']
 
-        expect(pane.getItems().length).toBe 3
-        expect(pane.getActiveItem()).toBe itemD
-        expect(pane.getActiveItem()).toBe pane.itemAtIndex(1)
-
-      it "keeps pending item when non-pending item is activated", ->
-        pane.activateItem(pane.itemAtIndex(0))
-
-        expect(pane.getItems().length).toBe 3
-        expect(pane.getActiveItem()).toBe pane.itemAtIndex(0)
+      it "adds the item after the active item if it is not pending", ->
+        pane.activateItem(itemC)
+        pane.activateItemAtIndex(2)
+        pane.activateItem(itemD)
+        expect(pane.getItems().map (item) -> item.name).toEqual ['A', 'B', 'D']
 
   describe "::activateNextItem() and ::activatePreviousItem()", ->
     it "sets the active item to the next/previous item, looping around at either end", ->

src/pane.coffee

@@ -365,6 +365,12 @@ class Pane extends Model
 
     return if item in @items
 
+    if item.isPending?()
+      for existingItem, i in @items
+        if existingItem.isPending?()
+          @destroyItem(existingItem)
+          break
+
     if typeof item.onDidDestroy is 'function'
       @itemSubscriptions.set item, item.onDidDestroy => @removeItem(item, false)