removed unsafe

Tests/Unit/SecureRandomTests.cs

@@ -0,0 +1,59 @@
+using System;
+using System.Linq;
+using Esiur.Misc;
+
+namespace Esiur.Tests.Unit;
+
+/// <summary>
+/// Guards the fix that moved Global.GenerateBytes / GenerateCode off System.Random onto a
+/// cryptographic RNG. These are sanity/entropy checks, not statistical proofs: their job is
+/// to fail loudly if someone reintroduces a predictable or constant generator.
+/// </summary>
+public class SecureRandomTests
+{
+    [Fact]
+    public void GenerateBytes_Returns_Requested_Length()
+    {
+        Assert.Equal(20, Global.GenerateBytes(20).Length);
+        Assert.Equal(0, Global.GenerateBytes(0).Length);
+    }
+
+    [Fact]
+    public void GenerateBytes_Are_Not_Repeated()
+    {
+        var a = Global.GenerateBytes(32);
+        var b = Global.GenerateBytes(32);
+        Assert.False(a.SequenceEqual(b), "Two nonces must not be identical.");
+    }
+
+    [Fact]
+    public void GenerateBytes_Are_Not_Constant()
+    {
+        var bytes = Global.GenerateBytes(64);
+        Assert.True(bytes.Distinct().Count() > 1, "Output must not be a single repeated byte.");
+    }
+
+    [Fact]
+    public void GenerateBytes_Have_Broad_Distribution()
+    {
+        // Across 4 KiB of output almost every byte value should appear at least once.
+        var bytes = Global.GenerateBytes(4096);
+        Assert.True(bytes.Distinct().Count() > 200,
+            "A cryptographic RNG should produce a wide spread of byte values.");
+    }
+
+    [Fact]
+    public void GenerateCode_Honours_Length_And_Alphabet()
+    {
+        const string alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
+        var code = Global.GenerateCode(24);
+        Assert.Equal(24, code.Length);
+        Assert.All(code, c => Assert.Contains(c, alphabet));
+    }
+
+    [Fact]
+    public void GenerateCode_Is_Not_Repeated()
+    {
+        Assert.NotEqual(Global.GenerateCode(24), Global.GenerateCode(24));
+    }
+}