[libc++][tests] Fix a test exercising incorrect overload

[pfusik]

I noticed a test I added in https://reviews.llvm.org/D153709 wasn't testing the constructor overload it was supposed to test. Instead, it tested the same overload as string-alloc.mode.pass.cpp.

[ldionne]

In D154489#4473185, @pfusik wrote:

I noticed a test I added in https://reviews.llvm.org/D153709 wasn't testing the constructor overload it was supposed to test. Instead, it tested the same overload as string-alloc.mode.pass.cpp.

I don't think that's true. The test was exercising this constructor: explicit basic_stringbuf(basic_string<charT, traits, Allocator>&& s, ios_base::openmode which = ios_base::in | ios_base::out) unless I missed something subtle. We're specifying a test allocator in the type of basic_stringbuf, but we're not passing any allocator to the constructor itself. Did I miss something?

[pfusik]

@ldionne std::basic_string<CharT, std::traits<CharT>, test_allocator<CharT>> is a different type than std::basic_string<CharT>.
I double-checked with printfs which constructor was called.

[pfusik]

@ldionne Can we please continue this review before the 17.0 branch is created?

The constructor to be tested is not a template and the allocator of the moved string must be the same type as stringbuf's allocator.
It was not: the string had a default std::allocator while stringbuf had test_allocator.
A different overload was selected that allows a different allocator and we have a different test for it.

[ldionne]

libcxx/test/std/input.output/string.streams/stringbuf/stringbuf.cons/string.move.mode.pass.cpp

29–36

OH!! I see it now. Okay, thanks for the fix.

What would you think about testing this thought?

std::basic_string<CharT, std::char_traits<CharT>, test_allocator<CharT>> s(STR("testing"));
const std::basic_stringbuf<CharT, std::char_traits<CharT>, test_allocator<CharT>> buf(std::move(s));
assert(buf.str() == STR("testing"));

It's nice to use the test_allocator and not just the default one.

[ldionne]

LGTM w/ suggestion and green CI

[pfusik]

Rebased. Added testing with test_allocator.

libcxx/test/std/input.output/string.streams/stringbuf/stringbuf.cons/string.move.mode.pass.cpp

 // class basic_stringbuf
 
 // explicit basic_stringbuf(basic_string<charT, traits, Allocator>&& s, ios_base::openmode which = ios_base::in | ios_base::out);
 
 #include <sstream>
 #include <cassert>
 
 #include "make_string.h"
-#include "test_allocator.h"
 #include "test_macros.h"
 
 #define STR(S) MAKE_STRING(CharT, S)
-#define SV(S) MAKE_STRING_VIEW(CharT, S)
 
 template <class CharT>
 static void test() {
   {
     std::basic_string<CharT> s(STR("testing"));
-    const std::basic_stringbuf<CharT, std::char_traits<CharT>, test_allocator<CharT>> buf(std::move(s));
-    assert(buf.view() == SV("testing"));
+    const std::basic_stringbuf<CharT> buf(std::move(s));
+    assert(buf.str() == STR("testing"));
   }
   {
     std::basic_string<CharT> s(STR("testing"));
-    const std::basic_stringbuf<CharT, std::char_traits<CharT>, test_allocator<CharT>> buf(
-        std::move(s), std::ios_base::out);
-    assert(buf.view() == SV("testing"));
+    const std::basic_stringbuf<CharT> buf(std::move(s), std::ios_base::out);
+    assert(buf.str() == STR("testing"));
   }
 }
 
 int main(int, char**) {
   test<char>();
 #ifndef TEST_HAS_NO_WIDE_CHARACTERS
   test<wchar_t>();
 #endif
   return 0;
 }