From f0135e93c5a5368527042a83a43cfdd323e33e8f Mon Sep 17 00:00:00 2001
From: Michael Nebel <michaelnebel@github.com>
Date: Wed, 14 Jan 2026 14:27:46 +0100
Subject: [PATCH] C#: Add a tests for MaybeNullExpr.

---
 .../dataflow/nullness/MaybeNullExpr.cs        | 21 +++++++++++++++++++
 .../dataflow/nullness/maybeNullExpr.expected  |  6 ++++++
 .../dataflow/nullness/maybeNullExpr.ql        |  6 ++++++
 .../library-tests/dataflow/nullness/options   |  2 ++
 4 files changed, 35 insertions(+)
 create mode 100644 csharp/ql/test/library-tests/dataflow/nullness/MaybeNullExpr.cs
 create mode 100644 csharp/ql/test/library-tests/dataflow/nullness/maybeNullExpr.expected
 create mode 100644 csharp/ql/test/library-tests/dataflow/nullness/maybeNullExpr.ql
 create mode 100644 csharp/ql/test/library-tests/dataflow/nullness/options

diff --git a/csharp/ql/test/library-tests/dataflow/nullness/MaybeNullExpr.cs b/csharp/ql/test/library-tests/dataflow/nullness/MaybeNullExpr.cs
new file mode 100644
index 00000000000..34c59df8bbd
--- /dev/null
+++ b/csharp/ql/test/library-tests/dataflow/nullness/MaybeNullExpr.cs
@@ -0,0 +1,21 @@
+using System;
+
+public class C
+{
+    string Prop { get; set; }
+
+    void M(object o, bool b)
+    {
+        // Conditional expr might be null.
+        var conditionalExpr = b ? new object() : null;
+
+        // Null-coalescing expr might be null as the right operand is null.
+        var nullCoalescing = o ?? null;
+
+        // Cast might be null.
+        var c = o as C;
+
+        // Conditional access might be null as the qualifier might be null.
+        var s1 = (o as C)?.Prop;
+    }
+}
diff --git a/csharp/ql/test/library-tests/dataflow/nullness/maybeNullExpr.expected b/csharp/ql/test/library-tests/dataflow/nullness/maybeNullExpr.expected
new file mode 100644
index 00000000000..4d8b00dd90c
--- /dev/null
+++ b/csharp/ql/test/library-tests/dataflow/nullness/maybeNullExpr.expected
@@ -0,0 +1,6 @@
+| MaybeNullExpr.cs:10:31:10:53 | ... ? ... : ... |
+| MaybeNullExpr.cs:10:50:10:53 | null |
+| MaybeNullExpr.cs:13:30:13:38 | ... ?? ... |
+| MaybeNullExpr.cs:13:35:13:38 | null |
+| MaybeNullExpr.cs:16:17:16:22 | ... as ... |
+| MaybeNullExpr.cs:19:19:19:24 | ... as ... |
diff --git a/csharp/ql/test/library-tests/dataflow/nullness/maybeNullExpr.ql b/csharp/ql/test/library-tests/dataflow/nullness/maybeNullExpr.ql
new file mode 100644
index 00000000000..3b5531ccb3a
--- /dev/null
+++ b/csharp/ql/test/library-tests/dataflow/nullness/maybeNullExpr.ql
@@ -0,0 +1,6 @@
+import csharp
+import semmle.code.csharp.dataflow.Nullness
+
+from MaybeNullExpr e
+where e.fromSource()
+select e
diff --git a/csharp/ql/test/library-tests/dataflow/nullness/options b/csharp/ql/test/library-tests/dataflow/nullness/options
new file mode 100644
index 00000000000..75c39b4541b
--- /dev/null
+++ b/csharp/ql/test/library-tests/dataflow/nullness/options
@@ -0,0 +1,2 @@
+semmle-extractor-options: /nostdlib /noconfig
+semmle-extractor-options: --load-sources-from-project:${testdir}/../../../resources/stubs/_frameworks/Microsoft.NETCore.App/Microsoft.NETCore.App.csproj