From 93d417049c4196d0dddc7cd58959c5c57c5505b6 Mon Sep 17 00:00:00 2001
From: Tom Hvitved <hvitved@github.com>
Date: Wed, 18 Feb 2026 08:41:13 +0100
Subject: [PATCH] C#: Add tests for `Equals` methods with nullable parameter
 types

---
 .../NullableTest.cs                           | 86 +++++++++++++++++++
 .../IncorrectEqualsSignature/NullableTest.cs  | 86 +++++++++++++++++++
 2 files changed, 172 insertions(+)
 create mode 100644 csharp/ql/test/query-tests/API Abuse/ClassDoesNotImplementEquals/NullableTest.cs
 create mode 100644 csharp/ql/test/query-tests/API Abuse/IncorrectEqualsSignature/NullableTest.cs

diff --git a/csharp/ql/test/query-tests/API Abuse/ClassDoesNotImplementEquals/NullableTest.cs b/csharp/ql/test/query-tests/API Abuse/ClassDoesNotImplementEquals/NullableTest.cs
new file mode 100644
index 000000000000..a66ffbec9a0f
--- /dev/null
+++ b/csharp/ql/test/query-tests/API Abuse/ClassDoesNotImplementEquals/NullableTest.cs	
@@ -0,0 +1,86 @@
+using System;
+
+#nullable enable
+
+namespace Test
+{
+    class TestClass1 : IEquatable<TestClass1>
+    {
+        private int field1;
+
+        public bool Equals(TestClass1? param1)
+        {
+            return param1 != null && field1 == param1.field1;
+        }
+
+        public override bool Equals(object? param2)
+        {
+            return param2 is TestClass1 tc && Equals(tc);
+        }
+
+        public override int GetHashCode()
+        {
+            return field1;
+        }
+    }
+
+    class TestClass2 : IEquatable<TestClass2>
+    {
+        private int field1;
+
+        public bool Equals(TestClass2 param1)
+        {
+            return param1 != null && field1 == param1.field1;
+        }
+
+        public override bool Equals(object? param2)
+        {
+            return param2 is TestClass2 tc && Equals(tc);
+        }
+
+        public override int GetHashCode()
+        {
+            return field1;
+        }
+    }
+
+    class TestClass3 : IEquatable<TestClass3>
+    {
+        private int field1;
+
+        public bool Equals(TestClass3? param1)
+        {
+            return param1 != null && field1 == param1.field1;
+        }
+
+        public override bool Equals(object param2)
+        {
+            return param2 is TestClass3 tc && Equals(tc);
+        }
+
+        public override int GetHashCode()
+        {
+            return field1;
+        }
+    }
+
+    class TestClass4 : IEquatable<TestClass4>
+    {
+        private int field1;
+
+        public bool Equals(TestClass4 param1)
+        {
+            return param1 != null && field1 == param1.field1;
+        }
+
+        public override bool Equals(object param2)
+        {
+            return param2 is TestClass4 tc && Equals(tc);
+        }
+
+        public override int GetHashCode()
+        {
+            return field1;
+        }
+    }
+}
\ No newline at end of file
diff --git a/csharp/ql/test/query-tests/API Abuse/IncorrectEqualsSignature/NullableTest.cs b/csharp/ql/test/query-tests/API Abuse/IncorrectEqualsSignature/NullableTest.cs
new file mode 100644
index 000000000000..a66ffbec9a0f
--- /dev/null
+++ b/csharp/ql/test/query-tests/API Abuse/IncorrectEqualsSignature/NullableTest.cs	
@@ -0,0 +1,86 @@
+using System;
+
+#nullable enable
+
+namespace Test
+{
+    class TestClass1 : IEquatable<TestClass1>
+    {
+        private int field1;
+
+        public bool Equals(TestClass1? param1)
+        {
+            return param1 != null && field1 == param1.field1;
+        }
+
+        public override bool Equals(object? param2)
+        {
+            return param2 is TestClass1 tc && Equals(tc);
+        }
+
+        public override int GetHashCode()
+        {
+            return field1;
+        }
+    }
+
+    class TestClass2 : IEquatable<TestClass2>
+    {
+        private int field1;
+
+        public bool Equals(TestClass2 param1)
+        {
+            return param1 != null && field1 == param1.field1;
+        }
+
+        public override bool Equals(object? param2)
+        {
+            return param2 is TestClass2 tc && Equals(tc);
+        }
+
+        public override int GetHashCode()
+        {
+            return field1;
+        }
+    }
+
+    class TestClass3 : IEquatable<TestClass3>
+    {
+        private int field1;
+
+        public bool Equals(TestClass3? param1)
+        {
+            return param1 != null && field1 == param1.field1;
+        }
+
+        public override bool Equals(object param2)
+        {
+            return param2 is TestClass3 tc && Equals(tc);
+        }
+
+        public override int GetHashCode()
+        {
+            return field1;
+        }
+    }
+
+    class TestClass4 : IEquatable<TestClass4>
+    {
+        private int field1;
+
+        public bool Equals(TestClass4 param1)
+        {
+            return param1 != null && field1 == param1.field1;
+        }
+
+        public override bool Equals(object param2)
+        {
+            return param2 is TestClass4 tc && Equals(tc);
+        }
+
+        public override int GetHashCode()
+        {
+            return field1;
+        }
+    }
+}
\ No newline at end of file