[libcxx] r287383 - [libcxx] [test] D26816: Fix non-Standard assumptions when testing sample().

[Stephan T. Lavavej via cfe-commits]

Author: stl_msft
Date: Fri Nov 18 15:54:43 2016
New Revision: 287383

URL: http://llvm.org/viewvc/llvm-project?rev=287383&view=rev
Log:
[libcxx] [test] D26816: Fix non-Standard assumptions when testing sample().

sample() isn't specified with a reproducible algorithm, so expecting
exact output is non-Standard. Mark those tests with LIBCPP_ASSERT.

In test_small_population(), we're guaranteed to get all of the elements,
but not necessarily in their original order. When PopulationCategory is
forward, we're guaranteed stability (and can therefore test equal()).
Otherwise, we can only test is_permutation(). (As it happens, both libcxx
and MSVC's STL provide stability in this scenario for input-only iterators.)

Modified:
    libcxx/trunk/test/std/algorithms/alg.modifying.operations/alg.random.sample/sample.pass.cpp

Modified: libcxx/trunk/test/std/algorithms/alg.modifying.operations/alg.random.sample/sample.pass.cpp
URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/test/std/algorithms/alg.modifying.operations/alg.random.sample/sample.pass.cpp?rev=287383&r1=287382&r2=287383&view=diff
==============================================================================
--- libcxx/trunk/test/std/algorithms/alg.modifying.operations/alg.random.sample/sample.pass.cpp (original)
+++ libcxx/trunk/test/std/algorithms/alg.modifying.operations/alg.random.sample/sample.pass.cpp Fri Nov 18 15:54:43 2016
@@ -19,9 +19,11 @@
 
 #include <algorithm>
 #include <random>
+#include <type_traits>
 #include <cassert>
 
 #include "test_iterators.h"
+#include "test_macros.h"
 
 struct ReservoirSampleExpectations {
   enum { os = 4 };
@@ -60,19 +62,23 @@ void test() {
   const unsigned os = Expectations::os;
   SampleItem oa[os];
   const int *oa1 = Expectations::oa1;
+  ((void)oa1); // Prevent unused warning
   const int *oa2 = Expectations::oa2;
+  ((void)oa2); // Prevent unused warning
   std::minstd_rand g;
   SampleIterator end;
   end = std::sample(PopulationIterator(ia),
                                   PopulationIterator(ia + is),
                                   SampleIterator(oa), os, g);
   assert(end.base() - oa == std::min(os, is));
-  assert(std::equal(oa, oa + os, oa1));
+  // sample() is deterministic but non-reproducible;
+  // its results can vary between implementations.
+  LIBCPP_ASSERT(std::equal(oa, oa + os, oa1));
   end = std::sample(PopulationIterator(ia),
                                   PopulationIterator(ia + is),
                                   SampleIterator(oa), os, std::move(g));
   assert(end.base() - oa == std::min(os, is));
-  assert(std::equal(oa, oa + os, oa2));
+  LIBCPP_ASSERT(std::equal(oa, oa + os, oa2));
 }
 
 template <template<class...> class PopulationIteratorType, class PopulationItem,
@@ -122,7 +128,12 @@ void test_small_population() {
                                   PopulationIterator(ia + is),
                                   SampleIterator(oa), os, g);
   assert(end.base() - oa == std::min(os, is));
-  assert(std::equal(oa, end.base(), oa1));
+  typedef typename std::iterator_traits<PopulationIterator>::iterator_category PopulationCategory;
+  if (std::is_base_of<std::forward_iterator_tag, PopulationCategory>::value) {
+    assert(std::equal(oa, end.base(), oa1));
+  } else {
+    assert(std::is_permutation(oa, end.base(), oa1));
+  }
 }
 
 int main() {