Comparing the various ways to run tests

What are the advantages and disadvantages of running NUnit on the tested 
assembly directly, rather than on an NUnit project or a Visual Studio 
project or solution?

I've always just created one assembly for my relatively simple projects, 
even if they are large, and organized via namespace in the test 
assembly.  Is it just that for projects that have more than one test 
assembly, an NUnit project or VS solution makes organization easier, or 
are there other benefits?

Brad 


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