Stop pages being checked again

If a page has no data, the next page defined in the task is selected to
continue building the task list. This removes pages from the list of
pages to check as the task list is being built, to ensure pages are not
checked twice through this.

server/utils/applications/forPagesInTask.test.ts

@@ -8,6 +8,7 @@ import { forPagesInTask } from './forPagesInTask'
 jest.mock('../journeyTypeFromArtifact')
 const FirstApplyPage = jest.fn()
 const SecondApplyPage = jest.fn()
+const ThirdApplyPage = jest.fn()
 const AssessPage = jest.fn()
 const PlacementRequestPage = jest.fn()
 
@@ -32,6 +33,7 @@ const applySection1Task1 = {
   pages: {
     first: FirstApplyPage,
     second: SecondApplyPage,
+    third: ThirdApplyPage,
   },
 }
 const applySection1Task2 = {
@@ -72,6 +74,7 @@ Apply.sections = [applySection1, applySection2]
 Apply.pages['first-apply-section-task-1'] = {
   first: FirstApplyPage,
   second: SecondApplyPage,
+  third: ThirdApplyPage,
 }
 
 const assessSection1Task1 = {
@@ -224,4 +227,35 @@ describe('forPagesInTask', () => {
       new Error('Page already visited while building task list: first. Visited pages: first, second'),
     )
   })
+
+  it('prevents a page being visited again through lack of previous page data', () => {
+    ;(journeyTypeFromArtifact as jest.MockedFunction<typeof journeyTypeFromArtifact>).mockReturnValue('applications')
+
+    const firstApplyPageInstance = {
+      next: () => 'third',
+    }
+    const secondApplyPageInstance = {
+      next: () => '',
+    }
+    const thirdApplyPageInstance = {
+      next: () => 'second',
+    }
+
+    FirstApplyPage.mockReturnValue(firstApplyPageInstance)
+    SecondApplyPage.mockReturnValue(secondApplyPageInstance)
+    ThirdApplyPage.mockReturnValue(thirdApplyPageInstance)
+    const spy = jest.fn()
+
+    const application = applicationFactory.build({
+      data: {
+        'first-apply-section-task-1': { first: { foo: 'bar' }, second: undefined, third: { bar: 'foo' } },
+      },
+    })
+
+    forPagesInTask(application, applySection1Task1, spy)
+
+    expect(spy).toHaveBeenCalledWith(firstApplyPageInstance, 'first')
+    expect(spy).toHaveBeenCalledWith(thirdApplyPageInstance, 'third')
+    expect(spy).toHaveBeenCalledTimes(2)
+  })
 })

server/utils/applications/forPagesInTask.ts

@@ -21,6 +21,7 @@ export const forPagesInTask = (
     }
 
     visited.push(pageName)
+    pageNames.splice(pageNames.indexOf(pageName), 1)
 
     const Page = getPage(task.id, pageName, journeyTypeFromArtifact(formArtifact))
     const body = formArtifact?.data?.[task.id]?.[pageName]