From 85b210955e7dd39dc914eeab0d49fc430c9b4796 Mon Sep 17 00:00:00 2001
From: Adam Luzsi <adamluzsi@gmail.com>
Date: Tue, 4 Jun 2024 20:25:19 +0200
Subject: [PATCH] improve panic message when invalid time range is given to
 random TimeBetween

---
 random/Random.go      |  7 +++++++
 random/Random_test.go | 21 +++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/random/Random.go b/random/Random.go
index 8c47629..5c43321 100644
--- a/random/Random.go
+++ b/random/Random.go
@@ -117,8 +117,15 @@ func (r *Random) StringNWithCharset(length int, charset string) string {
 	return string(bytes)
 }
 
+const panicInvalidTimeRangeMessage = `invalid time range given for TimeBetween, [to] time is earlier in time than [from] time.
+[from]: %s
+  [to]: %s`
+
 // TimeBetween returns, as an time.Time, a non-negative pseudo-random time in [from,to].
 func (r *Random) TimeBetween(from, to time.Time) time.Time {
+	if to.Before(from) {
+		panic(fmt.Sprintf(panicInvalidTimeRangeMessage, from.Format(time.RFC3339), to.Format(time.RFC3339)))
+	}
 	return time.Unix(int64(r.IntBetween(int(from.Unix()), int(to.Unix()))), 0).UTC()
 }
 
diff --git a/random/Random_test.go b/random/Random_test.go
index 3c90623..5439799 100644
--- a/random/Random_test.go
+++ b/random/Random_test.go
@@ -843,4 +843,25 @@ func SpecTimeBetween(s *testcase.Spec, rnd testcase.Var[*random.Random], sbj fun
 		t2, _ := time.Parse(time.RFC3339, t1.Format(time.RFC3339))
 		t.Must.Equal(t1.UTC(), t2.UTC())
 	})
+
+	s.And("till is smaller than from", func(s *testcase.Spec) {
+		fromTime.Let(s, func(t *testcase.T) time.Time {
+			return time.Date(2000, 1, 1, 12, 0, 0, 0, time.Local)
+		})
+		toTime.Let(s, func(t *testcase.T) time.Time {
+			return fromTime.Get(t).Add(-1 * time.Second)
+		})
+
+		s.Then("", func(t *testcase.T) {
+			out := assert.Panic(t, func() { subject(t) })
+			assert.NotNil(t, out)
+			panicMessage := fmt.Sprintf("%v", out)
+			assert.Contain(t, panicMessage, `invalid`)
+			assert.Contain(t, panicMessage, `[to]`)
+			assert.Contain(t, panicMessage, `earlier`)
+			assert.Contain(t, panicMessage, `[from]`)
+			assert.Contain(t, panicMessage, fromTime.Get(t).Format(time.RFC3339))
+			assert.Contain(t, panicMessage, toTime.Get(t).Format(time.RFC3339))
+		})
+	})
 }