1 files changed, 40 insertions, 0 deletions
diff --git a/src/math/rand/auto_test.go b/src/math/rand/auto_test.go
new file mode 100644
index 0000000..b057370
--- /dev/null
+++ b/src/math/rand/auto_test.go
@@ -0,0 +1,40 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package rand_test
+
+import (
+	. "math/rand"
+	"testing"
+)
+
+// This test is first, in its own file with an alphabetically early name,
+// to try to make sure that it runs early. It has the best chance of
+// detecting deterministic seeding if it's the first test that runs.
+
+func TestAuto(t *testing.T) {
+	// Pull out 10 int64s from the global source
+	// and then check that they don't appear in that
+	// order in the deterministic Seed(1) result.
+	var out []int64
+	for i := 0; i < 10; i++ {
+		out = append(out, Int63())
+	}
+
+	// Look for out in Seed(1)'s output.
+	// Strictly speaking, we should look for them in order,
+	// but this is good enough and not significantly more
+	// likely to have a false positive.
+	Seed(1)
+	found := 0
+	for i := 0; i < 1000; i++ {
+		x := Int63()
+		if x == out[found] {
+			found++
+			if found == len(out) {
+				t.Fatalf("found unseeded output in Seed(1) output")
+			}
+		}
+	}
+}