random: seed math/rand in one place with crypto strong seed #4783

This shouldn't be read as encouraging the use of math/rand instead of
crypto/rand in security sensitive contexts, rather as a safer default
if that does happen by accident.

lib/random/random_test.go

@@ -1,6 +1,7 @@
 package random
 
 import (
+	"math/rand"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -48,3 +49,16 @@ func TestPasswordDuplicates(t *testing.T) {
 		seen[s] = true
 	}
 }
+
+func TestSeed(t *testing.T) {
+	// seed 100 times and check the first random number doesn't repeat
+	// This test could fail with a probability of ~ 10**-15
+	const n = 100
+	var seen = map[int64]bool{}
+	for i := 0; i < n; i++ {
+		assert.NoError(t, Seed())
+		first := rand.Int63()
+		assert.False(t, seen[first])
+		seen[first] = true
+	}
+}