Add specs for toggling the gutter when the editor is hidden

spec/editor-component-spec.coffee

@@ -1589,6 +1589,36 @@ describe "EditorComponent", ->
       expect(horizontalScrollbarNode.scrollWidth).toBe editor.getScrollWidth()
       expect(horizontalScrollbarNode.style.left).toBe gutterNode.offsetWidth + 'px'
 
+    describe "when the editor is hidden", ->
+      hideEditorView = ->
+        wrapperNode.style.display = 'none'
+        expect(component.isVisible()).toBe false
+
+      showEditorView = ->
+        wrapperNode.style.display = 'block'
+        expect(component.isVisible()).toBe true
+
+      it "updates the position of the horizontal scrollbar only when the editor is visible", ->
+        # toggling gutter off
+        hideEditorView()
+        atom.config.set("editor.showLineNumbers", false)
+
+        showEditorView()
+        component.forceUpdate()
+        runSetImmediateCallbacks()
+        gutterNode = componentNode.querySelector('.gutter')
+        expect(horizontalScrollbarNode.style.left).toBe '0px'
+
+        # toggling gutter back on
+        hideEditorView()
+        atom.config.set("editor.showLineNumbers", true)
+
+        showEditorView()
+        component.forceUpdate()
+        runSetImmediateCallbacks()
+        gutterNode = componentNode.querySelector('.gutter')
+        expect(horizontalScrollbarNode.style.left).toBe gutterNode.offsetWidth + 'px'
+
   describe "mousewheel events", ->
     beforeEach ->
       atom.config.set('editor.scrollSensitivity', 100)