C#: Add test cases for operators.

Author: michaelnebel

csharp/ql/test/utils/model-generator/CaptureSummaryModels.expected

@@ -28,3 +28,5 @@
 | Summaries;IEnumerableFlow;false;ReturnFieldInIEnumerable;();Argument[Qualifier];ReturnValue;taint |
 | Summaries;IEnumerableFlow;false;ReturnIEnumerable;(System.Collections.Generic.IEnumerable<System.String>);Argument[0].Element;ReturnValue;taint |
 | Summaries;IEnumerableFlow;false;ReturnIEnumerableElement;(System.Collections.Generic.IEnumerable<System.Object>);Argument[0].Element;ReturnValue;taint |
+| Summaries;OperatorFlow;false;OperatorFlow;(System.Object);Argument[0];Argument[Qualifier];taint |
+| Summaries;OperatorFlow;false;op_Addition;(Summaries.OperatorFlow,Summaries.OperatorFlow);Argument[0];ReturnValue;taint |

csharp/ql/test/utils/model-generator/Summaries.cs

@@ -171,4 +171,39 @@ public int ReturnParam0(int input0, int input1)
     {
         return input0;
     }
+}
+
+public class OperatorFlow
+{
+    public readonly object Field;
+
+    public OperatorFlow(object o)
+    {
+        Field = o;
+    }
+
+    // Flow Summary.
+    public static OperatorFlow operator +(OperatorFlow a, OperatorFlow b)
+    {
+        return a;
+    }
+
+    // No flow summary.
+    public static OperatorFlow operator ++(OperatorFlow a)
+    {
+        return new OperatorFlow(new object());
+    }
+
+    // No flow summary as this is an implicit conversion operator.
+    public static implicit operator OperatorFlow(int i)
+    {
+        return new OperatorFlow(i);
+    }
+
+    // No flow summary as this is an explicit conversion operator.
+    public static explicit operator OperatorFlow(byte b)
+    {
+        return new OperatorFlow(b);
+    }
+
 }