Add test

math/rand/crypto_test.go

@@ -1,13 +1,30 @@
 package rand_test
 
 import (
+	crand "crypto/rand"
 	"fmt"
 	randv2 "math/rand/v2"
+	"strings"
 	"testing"
 
 	"github.com/itsubaki/neu/math/rand"
 )
 
+func ExampleRead() {
+	reader := crand.Reader
+	defer func() {
+		crand.Reader = reader
+	}()
+
+	crand.Reader = strings.NewReader("io.Reader stream to be read\n")
+	if _, err := rand.Read(); err != nil {
+		fmt.Println(err)
+	}
+
+	// Output:
+	// read: unexpected EOF
+}
+
 func TestMustRead(t *testing.T) {
 	v := randv2.New(rand.NewSource(rand.MustRead())).Float64()
 	if v >= 0 && v < 1 {