Quick spec for line number rendering

spec/text-editor-component-spec.js

@@ -2054,6 +2054,37 @@ describe('TextEditorComponent', () => {
       expect(decorationNode2.firstChild).toBeNull()
       expect(gutterB.getElement().firstChild.children.length).toBe(0)
     })
+
+    it('renders custom line number gutters', async () => {
+      const {component, editor} = buildComponent()
+      const gutterA = editor.addGutter({
+        name: 'a',
+        priority: 1,
+        type: 'line-number',
+        class: 'a-number',
+        labelFn: ({bufferRow}) => `a - ${bufferRow}`
+      })
+      const gutterB = editor.addGutter({
+        name: 'b',
+        priority: 1,
+        type: 'line-number',
+        class: 'b-number',
+        labelFn: ({bufferRow}) => `b - ${bufferRow}`
+      })
+      editor.setText('0000\n0001\n0002\n0003\n0004\n')
+
+      await component.getNextUpdatePromise()
+
+      const gutterAElement = gutterA.getElement()
+      const aNumbers = gutterAElement.querySelectorAll('div.line-number[data-buffer-row]')
+      const aLabels = Array.from(aNumbers, e => e.textContent)
+      expect(aLabels).toEqual(['a - 0', 'a - 1', 'a - 2', 'a - 3', 'a - 4', 'a - 5'])
+
+      const gutterBElement = gutterB.getElement()
+      const bNumbers = gutterBElement.querySelectorAll('div.line-number[data-buffer-row]')
+      const bLabels = Array.from(bNumbers, e => e.textContent)
+      expect(bLabels).toEqual(['b - 0', 'b - 1', 'b - 2', 'b - 3', 'b - 4', 'b - 5'])
+    })
   })
 
   describe('block decorations', () => {