feat: add test mode to quizzes and withhold its solutions

- mode, navigation and max_attempts columns with Go-side defaults
- classes.Withheld gates every solution field of the answer feedback
  and the attempt result while a test attempt is open
- a test's quiz detail lists no questions before the attempt starts
- admin fields and lang keys for the three settings

classes/policy.go

@@ -0,0 +1,15 @@
+package classes
+
+import "git.golem15.com/golem15/sm-quizzes-plugin/models"
+
+// IsTest reports whether the quiz runs as a test. A zero or unknown mode is
+// learning, so a quiz written before test mode existed keeps its behaviour.
+func IsTest(q *models.Quiz) bool { return q != nil && q.Mode == models.ModeTest }
+
+// Withheld reports whether an attempt's solutions must stay hidden: it is
+// an attempt at a test that is not finished yet. Every student serializer
+// drops is_correct, points, correct answers, explanations and model answers
+// while it is true.
+func Withheld(a *models.Attempt) bool {
+	return a != nil && IsTest(a.Quiz) && a.CompletedAt == nil
+}

classes/policy_test.go

@@ -0,0 +1,39 @@
+package classes_test
+
+import (
+	"testing"
+	"time"
+
+	"git.golem15.com/golem15/sm-quizzes-plugin/classes"
+	"git.golem15.com/golem15/sm-quizzes-plugin/models"
+)
+
+func TestIsTestAndWithheld(t *testing.T) {
+	if classes.IsTest(nil) {
+		t.Error("IsTest(nil) = true")
+	}
+	for mode, want := range map[string]bool{"": false, models.ModeLearning: false, "exam": false, models.ModeTest: true} {
+		if got := classes.IsTest(&models.Quiz{Mode: mode}); got != want {
+			t.Errorf("IsTest(mode %q) = %v, want %v", mode, got, want)
+		}
+	}
+	done := time.Now()
+	test, learning := &models.Quiz{Mode: models.ModeTest}, &models.Quiz{Mode: models.ModeLearning}
+	cases := []struct {
+		name string
+		a    *models.Attempt
+		want bool
+	}{
+		{"open test", &models.Attempt{Quiz: test}, true},
+		{"completed test", &models.Attempt{Quiz: test, CompletedAt: &done}, false},
+		{"open learning", &models.Attempt{Quiz: learning}, false},
+		{"zero mode", &models.Attempt{Quiz: &models.Quiz{}}, false},
+		{"nil attempt", nil, false},
+		{"nil quiz", &models.Attempt{}, false},
+	}
+	for _, tc := range cases {
+		if got := classes.Withheld(tc.a); got != tc.want {
+			t.Errorf("Withheld(%s) = %v, want %v", tc.name, got, tc.want)
+		}
+	}
+}

classes/service.go

@@ -258,6 +258,10 @@ type Feedback struct {
 	Question         models.Question
 	Result           ScoreResult
 	CorrectAnswerIDs []uint
+	// Withheld is set for an open test attempt: the solutions stay hidden
+	// and the serializer must drop Result, CorrectAnswerIDs and every
+	// solution field of Question.
+	Withheld bool
 }
 
 // Answer records or overwrites the user's answer to one question of an
@@ -334,7 +338,7 @@ func (s *Service) Answer(ctx context.Context, userID, attemptID uint, in AnswerI
 		}).Create(&row).Error; err != nil {
 			return err
 		}
-		fb = &Feedback{Question: question, Result: res, CorrectAnswerIDs: correct}
+		fb = &Feedback{Question: question, Result: res, CorrectAnswerIDs: correct, Withheld: Withheld(attempt)}
 		return nil
 	})
 	if err != nil {