Made test program consist of two source files.

test cases/csharp/1 basic/meson.build

@@ -1,4 +1,4 @@
 project('simple c#', 'cs')
 
-e = executable('prog', 'prog.cs', install : true)
+e = executable('prog', 'prog.cs', 'text.cs', install : true)
 test('basic', e)

test cases/csharp/1 basic/prog.cs

@@ -2,6 +2,7 @@ using System;
 
 public class Prog {
     static public void Main () {
-        Console.WriteLine("C# is working.");
+        TextGetter tg = new TextGetter();
+        Console.WriteLine(tg.getText());
     }
 }

test cases/csharp/1 basic/text.cs

@@ -0,0 +1,7 @@
+using System;
+
+public class TextGetter {
+    public String getText() {
+        return "C# is working.";
+    }
+}