fix bug in metrics first/last calculation if second arg was zero

report/metrics.go

@@ -79,14 +79,14 @@ func (m Metric) Len() int {
 }
 
 func first(t1, t2 time.Time) time.Time {
-	if !t1.IsZero() && t1.Before(t2) {
+	if t2.IsZero() || (!t1.IsZero() && t1.Before(t2)) {
 		return t1
 	}
 	return t2
 }
 
 func last(t1, t2 time.Time) time.Time {
-	if !t1.IsZero() && t1.After(t2) {
+	if t2.IsZero() || (!t1.IsZero() && t1.After(t2)) {
 		return t1
 	}
 	return t2

report/metrics_internal_test.go

@@ -0,0 +1,29 @@
+package report
+
+import (
+	"testing"
+	"time"
+)
+
+func TestFirstLast(t *testing.T) {
+	zero, t1, t2 := time.Time{}, time.Now(), time.Now().Add(1*time.Minute)
+	tests := []struct {
+		arg1, arg2, first, last time.Time
+	}{
+		{zero, zero, zero, zero},
+		{t1, zero, t1, t1},
+		{zero, t1, t1, t1},
+		{t1, t1, t1, t1},
+		{t1, t2, t1, t2},
+		{t2, t1, t1, t2},
+	}
+	for _, test := range tests {
+		if got := first(test.arg1, test.arg2); !got.Equal(test.first) {
+			t.Errorf("first(%q, %q) => %q, Expected: %q", test.arg1, test.arg2, got, test.first)
+		}
+
+		if got := last(test.arg1, test.arg2); !got.Equal(test.last) {
+			t.Errorf("last(%q, %q) => %q, Expected: %q", test.arg1, test.arg2, got, test.last)
+		}
+	}
+}