Add variable question distractor pools

api/QuestionsApi.Tests/ChoicePoolTests.cs

@@ -0,0 +1,104 @@
+using QuestionsApi.Models;
+using QuestionsApi.Services;
+using Xunit;
+
+namespace QuestionsApi.Tests;
+
+public sealed class ChoicePoolTests
+{
+    [Fact]
+    public void LegacyResponseContainsFiveChoicesAndAlwaysIncludesCorrectAnswer()
+    {
+        var question = BuildQuestion(9);
+
+        for (var iteration = 0; iteration < 50; iteration++)
+        {
+            var response = QuestionResponse.FromModel(question, includeChoicePool: false);
+            Assert.Equal(5, response.Choices.Count);
+            Assert.Equal(5, response.Choices.Select(choice => choice.Id).Distinct().Count());
+            Assert.Contains(response.Choices, choice => choice.Id == question.CorrectChoiceId);
+            Assert.All(response.ChoiceExplanations.Keys, id => Assert.Contains(response.Choices, choice => choice.Id == id));
+            Assert.All(response.WrongAnswerFollowups.Keys, id => Assert.Contains(response.Choices, choice => choice.Id == id));
+        }
+    }
+
+    [Fact]
+    public void PoolCapableResponseContainsCompletePool()
+    {
+        var question = BuildQuestion(9);
+        var response = QuestionResponse.FromModel(question, includeChoicePool: true);
+        Assert.Equal(9, response.Choices.Count);
+    }
+
+    [Fact]
+    public void PublishedQuestionRequiresCompletePerChoiceTeachingContent()
+    {
+        var request = BuildRequest(6);
+        Assert.Null(QuestionValidator.Validate(request));
+
+        request.WrongAnswerFollowups.Remove("F");
+        Assert.Contains("every incorrect choice", QuestionValidator.Validate(request));
+    }
+
+    [Fact]
+    public void PublishedQuestionRequiresAtLeastFiveUniqueChoices()
+    {
+        var request = BuildRequest(4);
+        Assert.Contains("at least five", QuestionValidator.Validate(request));
+
+        request = BuildRequest(5);
+        request.Choices[4].Id = "A";
+        Assert.Contains("unique", QuestionValidator.Validate(request));
+    }
+
+    private static Question BuildQuestion(int count)
+    {
+        var request = BuildRequest(count);
+        return new Question
+        {
+            ExternalId = request.ExternalId,
+            Stem = request.Stem,
+            LeadIn = request.LeadIn,
+            Choices = request.Choices,
+            CorrectChoiceId = request.CorrectChoiceId,
+            Explanation = request.Explanation,
+            ChoiceExplanations = request.ChoiceExplanations,
+            WrongAnswerFollowups = request.WrongAnswerFollowups,
+            ChoiceSelectionPercentages = request.ChoiceSelectionPercentages
+        };
+    }
+
+    private static UpsertQuestionRequest BuildRequest(int count)
+    {
+        var ids = Enumerable.Range(0, count).Select(index => ((char)('A' + index)).ToString()).ToList();
+        var choices = ids.Select(id => new QuestionChoice { Id = id, Text = $"Choice {id}" }).ToList();
+        return new UpsertQuestionRequest
+        {
+            ExternalId = "choice-pool-test",
+            Stem = "A complete clinical vignette.",
+            LeadIn = "Which option is most appropriate?",
+            Choices = choices,
+            CorrectChoiceId = "A",
+            Explanation = "Explanation",
+            ChoiceExplanations = ids.ToDictionary(id => id, id => id == "A" ? "Correct." : "Incorrect."),
+            WrongAnswerFollowups = ids.Where(id => id != "A").ToDictionary(
+                id => id,
+                id => new WrongAnswerFollowup
+                {
+                    Prompt = "Which finding makes this less appropriate?",
+                    Choices =
+                    [
+                        new QuestionChoice { Id = "A", Text = "Finding one" },
+                        new QuestionChoice { Id = "B", Text = "Finding two" }
+                    ],
+                    CorrectChoiceId = "A",
+                    TeachingPoint = "Teaching point"
+                }),
+            ChoiceSelectionPercentages = ids.ToDictionary(id => id, _ => 0),
+            Discipline = "Medicine",
+            System = "Cardiovascular System",
+            Difficulty = 2,
+            IsPublished = true
+        };
+    }
+}

api/QuestionsApi.Tests/QuestionsApi.Tests.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
+    <PackageReference Include="xunit" Version="2.9.2" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2" />
+    <ProjectReference Include="..\QuestionsApi\QuestionsApi.csproj" />
+  </ItemGroup>
+</Project>