sioutil: add tests for Random and MustRandom

This commit adds two unit tests for `Random` and
`MustRandom`.

The main purpose of the unit tests is to ensure that
`sioutil.Random(0)` behaves as expected.

sioutil/sio_test.go

@@ -0,0 +1,31 @@
+// Copyright (c) 2019 Andreas Auernhammer. All rights reserved.
+// Use of this source code is governed by a license that can be
+// found in the LICENSE file.
+
+package sioutil
+
+import "testing"
+
+func TestRandom(t *testing.T) {
+	b, err := Random(0)
+	if err != nil || len(b) != 0 {
+		t.Fatalf("Failed to generate empty slice: %v - got %d - want %d", err, len(b), 0)
+	}
+
+	b, err = Random(16)
+	if err != nil || len(b) != 16 {
+		t.Fatalf("Failed to generate empty slice: %v - got %d - want %d", err, len(b), 16)
+	}
+}
+
+func TestMustRandom(t *testing.T) {
+	b := MustRandom(0)
+	if len(b) != 0 {
+		t.Fatalf("Failed to generate empty slice: got %d - want %d", len(b), 0)
+	}
+
+	b = MustRandom(16)
+	if len(b) != 16 {
+		t.Fatalf("Failed to generate random slice: got %d - want %d", len(b), 16)
+	}
+}