Changes from code review

Author: CharliePoole

src/NUnitCommon/nunit.agent.core/AgentOptions.cs

@@ -49,11 +49,10 @@ public AgentOptions(params string[] args)
                         val = option.Substring(delim + 1);
                     }
 
-                    if (!VALID_OPTIONS.ContainsKey(opt))
+                    // Simultaneously check that the option is valid and determine if it takes an argument
+                    if (!VALID_OPTIONS.TryGetValue(opt, out bool optionTakesValue))
                         throw new Exception($"Invalid argument: {arg}");
 
-                    bool optionTakesValue = VALID_OPTIONS[opt];
-
                     if (optionTakesValue)
                     {
                         if (val == null && index + 1 < args.Length)
@@ -119,7 +118,7 @@ string GetArgumentValue(string argument)
 
         private static bool IsOption(string arg)
         {
-            return arg.StartsWith("--");
+            return arg.StartsWith("--", StringComparison.Ordinal);
         }
     }
 }