From 8ac05b458e152b819b8c3827d35398edd8b7d3f7 Mon Sep 17 00:00:00 2001
From: PJ <ipriyanshujain@gmail.com>
Date: Mon, 1 Jun 2026 13:58:45 +0530
Subject: [PATCH] test(ltl): lock violation witness reason, IsError, and step

---
 internal/ltl/witness_test.go | 80 ++++++++++++++++++++++++++++++++++++
 1 file changed, 80 insertions(+)
 create mode 100644 internal/ltl/witness_test.go

diff --git a/internal/ltl/witness_test.go b/internal/ltl/witness_test.go
new file mode 100644
index 0000000..6e4c580
--- /dev/null
+++ b/internal/ltl/witness_test.go
@@ -0,0 +1,80 @@
+package ltl
+
+import (
+	"errors"
+	"testing"
+	"time"
+)
+
+func TestViolation_PredicateFalseCarriesReasonAndStep(t *testing.T) {
+	values := []bool{true, false}
+	step := 0
+	evaluator := NewEvaluator(Always(ThunkNamed("p", func() (bool, error) {
+		current := values[step]
+		step++
+		return current, nil
+	})))
+	if got := evaluator.ObserveAt(time.Unix(0, 0)); got != VerdictHolds {
+		t.Fatalf("step 1: got %v, want holds", got)
+	}
+	if got := evaluator.ObserveAt(time.Unix(1, 0)); got != VerdictViolated {
+		t.Fatalf("step 2: got %v, want violated", got)
+	}
+	witness := evaluator.Violation()
+	if witness == nil {
+		t.Fatal("Violation = nil, want non-nil")
+	}
+	if witness.Reason != "predicate false" {
+		t.Errorf("Reason = %q, want %q", witness.Reason, "predicate false")
+	}
+	if witness.Step != 2 {
+		t.Errorf("Step = %d, want 2", witness.Step)
+	}
+	if witness.IsError {
+		t.Errorf("IsError = true, want false for a plain false")
+	}
+}
+
+func TestViolation_ThrownPredicateSetsIsError(t *testing.T) {
+	evaluator := NewEvaluator(Always(ThunkNamed("p", func() (bool, error) {
+		return false, errors.New("boom")
+	})))
+	if got := evaluator.Observe(); got != VerdictViolated {
+		t.Fatalf("got %v, want violated", got)
+	}
+	witness := evaluator.Violation()
+	if witness == nil {
+		t.Fatal("Violation = nil, want non-nil")
+	}
+	if !witness.IsError {
+		t.Errorf("IsError = false, want true for a thrown predicate")
+	}
+	if witness.Reason != "boom" {
+		t.Errorf("Reason = %q, want %q", witness.Reason, "boom")
+	}
+}
+
+func TestViolation_FinalizeFillsWitness(t *testing.T) {
+	evaluator := NewEvaluator(Eventually(ThunkNamed("p", func() (bool, error) {
+		return false, nil
+	})))
+	evaluator.ObserveAt(time.Unix(0, 0))
+	if got := evaluator.Finalize(); got != VerdictViolated {
+		t.Fatalf("Finalize = %v, want violated", got)
+	}
+	witness := evaluator.Violation()
+	if witness == nil {
+		t.Fatal("Violation = nil after Finalize, want non-nil")
+	}
+	if witness.Reason != "eventually never satisfied" {
+		t.Errorf("Reason = %q, want %q", witness.Reason, "eventually never satisfied")
+	}
+}
+
+func TestViolation_NilBeforeViolation(t *testing.T) {
+	evaluator := NewEvaluator(Always(Pure(true)))
+	evaluator.Observe()
+	if got := evaluator.Violation(); got != nil {
+		t.Errorf("Violation = %+v, want nil for a holding run", got)
+	}
+}