Fixed translation of required Form questions (#73)

# Fixed translation of required Form questions

## ♻️ Current situation & Problem
As reported in #71 the requiredness of groups is not correctly mapped to
ResearchKit Forms. There are two mistakes here:
1. The `isOptional` property of the individual `ORKFormItem` is invested
(this controls if the "Continue" button is rendered enabled or disabled)
2. The `isOptional` property of the `ORKFormStep` is never set (controls
the appearance of the "Skip" button).


## ⚙️ Release Notes 
* Fixed an issue where you could skip required questions in a when
rendered as a Form.


## 📚 Documentation
Added inline docs to explain the different semantics of the two
`isOptional` properties.


## ✅ Testing
Added UI tests to verify this behavior. Our existing `Form Example` FHIR
questionnaire had a Form with 3 question out of which 2 are required. We
ensure that the Skip button doesn't show up and the Next Button is only
enabled once all the required question are answered.


### Code of Conduct & Contributing Guidelines 

By submitting creating this pull request, you agree to follow our [Code
of
Conduct](https://github.com/StanfordBDHG/.github/blob/main/CODE_OF_CONDUCT.md)
and [Contributing
Guidelines](https://github.com/StanfordBDHG/.github/blob/main/CONTRIBUTING.md):
- [x] I agree to follow the [Code of
Conduct](https://github.com/StanfordBDHG/.github/blob/main/CODE_OF_CONDUCT.md)
and [Contributing
Guidelines](https://github.com/StanfordBDHG/.github/blob/main/CONTRIBUTING.md).

CITATION.cff

@@ -18,6 +18,9 @@ authors:
 - family-names: "Aalami"
   given-names: "Oliver"
   orcid: "https://orcid.org/0000-0002-7799-2429"
+- family-names: "Bauer"
+  given-names: "Andreas"
+  orcid: "https://orcid.org/0000-0002-1680-237X"
 title: "ResearchKitOnFHIR"
 doi: 10.5281/zenodo.7538169
 url: "https://github.com/StanfordBDHG/ResearchKitOnFHIR"

CONTRIBUTORS.md

@@ -15,3 +15,4 @@ ResearchKitOnFHIR contributors
 
 * [Vishnu Ravi](https://github.com/vishnuravi)
 * [Paul Schmiedmayer](https://github.com/PSchmiedmayer)
+* [Andreas Bauer](https://github.com/Supereg)

Example/ExampleUITests/ExampleUITests.swift

@@ -301,8 +301,19 @@ final class ExampleUITests: XCTestCase {
         app.buttons["Get Started"].tap()
 
         // Answer the three questions
+
         app.tables.staticTexts["Yes"].tap()
+
+
+        // The first two questions are required ones, the last one is optional.
+        // Tests that the button is disabled just before we answer the last required question.
+        XCTAssert(app.buttons["Next"].exists)
+        XCTAssertFalse(app.buttons["Next"].isEnabled)
+        XCTAssertFalse(app.buttons["Skip"].exists)
+
         app.tables.staticTexts["Chocolate"].tap()
+        XCTAssert(app.buttons["Next"].isEnabled)
+
         app.tables.staticTexts["Sprinkles"].tap()
         app.tables.staticTexts["Marshmallows"].tap()
         app.buttons["Next"].tap()

Sources/ResearchKitOnFHIR/FHIRToResearchKit/QuestionnaireItem+ResearchKit.swift

@@ -92,7 +92,9 @@ extension QuestionnaireItem {
         formStep.title = title
         formStep.text = text?.value?.string ?? ""
         var formItems = [ORKFormItem]()
-
+
+        var containsRequiredSteps = false
+
         for question in nestedQuestions {
             guard let questionId = question.linkId.value?.string,
                   let questionText = question.text?.value?.string,
@@ -102,13 +104,20 @@ extension QuestionnaireItem {
 
             let formItem = ORKFormItem(identifier: questionId, text: questionText, answerFormat: answerFormat)
             if let required = question.required?.value?.bool {
-                formItem.isOptional = required
+                // if !optional, the `Continue` will stay disabled till the question is answered.
+                formItem.isOptional = !required
+
+                if required {
+                    containsRequiredSteps = true
+                }
             }
 
             formItems.append(formItem)
         }
 
         formStep.formItems = formItems
+        // if optional, the `Next` button will appear
+        formStep.isOptional = !containsRequiredSteps
         return formStep
     }