C#: Add more tests for `cs/constant-condition`

csharp/ql/test/query-tests/Bad Practices/Control-Flow/ConstantCondition/ConstantCondition.cs

@@ -1,4 +1,4 @@
-// semmle-extractor-options: /r:System.Threading.Thread.dll /r:System.Diagnostics.Debug.dll
+// semmle-extractor-options: /r:System.Threading.Thread.dll /r:System.Diagnostics.Debug.dll /langversion:preview
 
 using System;
 using System.Collections;
@@ -89,6 +89,23 @@ class ConstantMatching
               break;
         }
     }
+
+    string M4(object o)
+    {
+        return o switch
+        {
+            _ => o.ToString() // BAD
+        };
+    }
+
+    string M5(object o)
+    {
+        return o switch
+        {
+            "" => " ",
+            _ => o.ToString() // GOOD
+        };
+    }
 }
 
 class Assertions

csharp/ql/test/query-tests/Bad Practices/Control-Flow/ConstantCondition/ConstantCondition.expected

@@ -7,6 +7,8 @@
 | ConstantCondition.cs:64:18:64:18 | 2 | Pattern never matches. |
 | ConstantCondition.cs:66:18:66:18 | 3 | Pattern always matches. |
 | ConstantCondition.cs:77:18:77:20 | access to type Int32 | Pattern never matches. |
+| ConstantCondition.cs:97:13:97:13 | _ | Pattern always matches. |
+| ConstantCondition.cs:106:13:106:13 | _ | Pattern always matches. |
 | ConstantConditionBad.cs:5:16:5:20 | ... > ... | Condition always evaluates to 'false'. |
 | ConstantConditionalExpressionCondition.cs:11:22:11:34 | ... == ... | Condition always evaluates to 'true'. |
 | ConstantConditionalExpressionCondition.cs:12:21:12:25 | false | Condition always evaluates to 'false'. |