[LNT] Python 3 support: stable showtests output

[thopre]

Summary

lnt showtests output depends on the iteration order of a set, which has
no guarantee whatsoever. This makes the result of test
tests/lnttool/showtests.shtest unstable in particular accross Python 2
and 3. This commit makes the lnt.tests constructor return a new sorted
list instead of the set, thus guaranteeing a stable output of lnt
showtests. It also lists tests in alphabetical order which makes it
nicer for users.

[hubert.reinterpretcast]

My general impression is that this is harmless. As it is, there is no other key available to sort on. @cmatthews, can you confirm?

[thopre]

In D68220#1688136, @hubert.reinterpretcast wrote:

My general impression is that this is harmless. As it is, there is no other key available to sort on. @cmatthews, can you confirm?

Ping @cmatthews ?

[cmatthews]

Yeah, that seems fine.

lnt/tests/__init__.py

 """
 Access to built-in tests.
 """
 # FIXME: There are better ways to do this, no doubt. We also would like this to
 # be extensible outside of the installation. Lookup how 'nose' handles this.
 
 _known_tests = set(['compile', 'nt', 'test_suite'])
 
 
 def get_names():
     """get_test_names() -> list
 
     Return the list of known built-in test names.
     """
-    return _known_tests
+    return sorted(_known_tests)
 
 
 def get_module(name):
     import importlib
     """get_test_instance(name) -> lnt.test.BuiltinTest
 
     Return an instance of the named test.
     """

tests/lnttool/showtests.shtest

 # RUN: lnt showtests | FileCheck %s
 # CHECK: Available tests:
 # CHECK-NEXT: compile    - Single file compile-time performance testing
-# CHECK-NEXT: test_suite - LLVM test-suite
 # CHECK-NEXT: nt         - LLVM test-suite compile and execution tests
+# CHECK-NEXT: test_suite - LLVM test-suite