fix(trace): invert ConvergenceRate so higher means faster

internal/trace/trace.go

@@ -101,7 +101,9 @@ func (t *Trace) computeSummary() *Summary {
 			}
 		}
 		if firstSuccess > 0 {
-			s.ConvergenceRate = float64(firstSuccess) / float64(s.TotalIterations)
+			// Higher is better: success on the first iteration => 1.0,
+			// success only on the last iteration => near 0.
+			s.ConvergenceRate = 1.0 - float64(firstSuccess-1)/float64(s.TotalIterations)
 		}
 	}
 

internal/trace/trace_test.go

@@ -0,0 +1,52 @@
+package trace
+
+import "testing"
+
+func TestConvergenceRateHigherMeansFaster(t *testing.T) {
+	fast := New([]Iteration{
+		{Number: 1, Verification: &Verification{Status: "success"}},
+		{Number: 2, Verification: &Verification{Status: "success"}},
+		{Number: 3, Verification: &Verification{Status: "fail"}},
+		{Number: 4},
+		{Number: 5},
+		{Number: 6},
+		{Number: 7},
+		{Number: 8},
+		{Number: 9},
+		{Number: 10},
+	})
+	slow := New([]Iteration{
+		{Number: 1, Verification: &Verification{Status: "fail"}},
+		{Number: 2, Verification: &Verification{Status: "fail"}},
+		{Number: 3, Verification: &Verification{Status: "fail"}},
+		{Number: 4, Verification: &Verification{Status: "fail"}},
+		{Number: 5, Verification: &Verification{Status: "fail"}},
+		{Number: 6, Verification: &Verification{Status: "fail"}},
+		{Number: 7, Verification: &Verification{Status: "fail"}},
+		{Number: 8, Verification: &Verification{Status: "fail"}},
+		{Number: 9, Verification: &Verification{Status: "fail"}},
+		{Number: 10, Verification: &Verification{Status: "success"}},
+	})
+
+	if fast.Summary.ConvergenceRate != 1.0 {
+		t.Fatalf("first-try ConvergenceRate = %v, want 1.0", fast.Summary.ConvergenceRate)
+	}
+	wantSlow := 1.0 - float64(9)/float64(10)
+	if slow.Summary.ConvergenceRate != wantSlow {
+		t.Fatalf("last-try ConvergenceRate = %v, want %v", slow.Summary.ConvergenceRate, wantSlow)
+	}
+	if !(fast.Summary.ConvergenceRate > slow.Summary.ConvergenceRate) {
+		t.Fatalf("expected faster convergence to score higher: fast=%v slow=%v",
+			fast.Summary.ConvergenceRate, slow.Summary.ConvergenceRate)
+	}
+}
+
+func TestConvergenceRateNoSuccessIsZero(t *testing.T) {
+	tr := New([]Iteration{
+		{Number: 1, Verification: &Verification{Status: "fail"}},
+		{Number: 2, Verification: &Verification{Status: "fail"}},
+	})
+	if tr.Summary.ConvergenceRate != 0 {
+		t.Fatalf("ConvergenceRate = %v, want 0 when never successful", tr.Summary.ConvergenceRate)
+	}
+}