Hi Huong,
AQtime can profile both native and managed code. So, you can perform coverage testing of your server application. To do this, configure the [url=http://support.smartbear.com/viewarticle/43496/]Coverage[/url] profiler for your application and run the profiling when you start your tests from the client side. Please go through the [url=http://support.smartbear.com/viewarticle/42989/]Coverage Profiler Tutorial[/url] - it contains the information you need.
If you also need to get your unit tests' code coverage, you can profile your test assemblies that are loaded to the [i]nunit.exe[/i] or [i]nunit-console.exe[/i] process as described in the [url=http://support.smartbear.com/viewarticle/42960/]Profiling .NET Applications[/url] article. One thing should be noted: by default, NUnit copies assemblies with tests to temporary folders and loads the assemblies from the folders, so, in fact, both [i]nunit.exe[/i] and [i]nunit-console.exe[/i] processes do not load original assemblies. I suggest that you disable the [b]Enable Shadow Copy[/b] option in the GUI NUnit program ([i]Tools | Settings... | Test Loader | Advanced[/i]) and specify the [b]/noshadow[/b] option for the [i]nunit-console[/i] program to prevent this behavior.
I hope this helps.