Assuming you are using Console.WriteLine to output the lines...
NUnit 3 groups all output with the test result. Of course, the test
result is not available until after the test is finished. Your Test1
naturally finishes before the containing fixture finishes, so the
order of display is reversed.
If you want to see output at the time it is produced, NUnit 3.6.1 also
supports "immediate" output, appears right away, without waiting for
the test to end.
"Normal" (end of test) output is produced by:
* Console.Write(Line)
* TestContext.Write(Line)
Immediate output is produced by:
* Console.Error.Write(Line)
* TestContext.Error.Write(Line)
* TestContext.Progress.Write(Line)