Fix memory leaks in cc/Log_* tests

runtime/vm/log_test.cc

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"
 
 #include "include/dart_tools_api.h"
 #include "vm/dart_api_impl.h"
 #include "vm/dart_entry.h"
 #include "vm/debugger.h"
 #include "vm/globals.h"
 #include "vm/isolate.h"
 #include "vm/log.h"
 #include "vm/message_handler.h"
 #include "vm/unit_test.h"
 
 namespace dart {
 
-static const char* test_output_;
+static const char* test_output_ = NULL;
 static void TestPrinter(const char* format, ...) {
   // Measure.
   va_list args;
   va_start(args, format);
   intptr_t len = OS::VSNPrint(NULL, 0, format, args);
   va_end(args);
 
   // Print string to buffer.
   char* buffer = reinterpret_cast<char*>(malloc(len + 1));
   va_list args2;
   va_start(args2, format);
   OS::VSNPrint(buffer, (len + 1), format, args2);
   va_end(args2);
 
-  // Leaks buffer.
+  if (test_output_ != NULL) {
+    free(const_cast<char*>(test_output_));
+    test_output_ = NULL;
+  }
   test_output_ = buffer;
 }
 
 class LogTestHelper : public AllStatic {
  public:
   static void SetPrinter(Log* log, LogPrinter printer) {
     ASSERT(log != NULL);
     ASSERT(printer != NULL);
     log->printer_ = printer;
   }
+
+  static void FreeTestOutput() {
+    if (test_output_ != NULL) {

[Vyacheslav Egorov (Google), 2017/01/24 16:10:51]

No need to check if it is not NULL - free(NULL) is safe.

+      free(const_cast<char*>(test_output_));
+      test_output_ = NULL;
+    }
+  }
 };
 
 
 TEST_CASE(Log_Macro) {
   test_output_ = NULL;
   Log* log = Log::Current();
   LogTestHelper::SetPrinter(log, TestPrinter);
 
   THR_Print("Hello %s", "World");
   EXPECT_STREQ("Hello World", test_output_);
   THR_Print("SingleArgument");
   EXPECT_STREQ("SingleArgument", test_output_);
+  LogTestHelper::FreeTestOutput();
 }
 
 
 TEST_CASE(Log_Basic) {
   test_output_ = NULL;

[Vyacheslav Egorov (Google), 2017/01/24 16:10:51]

Some sort of scoped object might be a better way to manage this. 

TestOutputHelper helper;
TestOutputHelper helper(log);  // if log needs to be deleted too.

something along these lines:

class TOH {
  explicit TOH(Log* log = NULL) : log_(log) { test_output_ = NULL; }
  ~TOH() { free(test_output_); delete log_; }
}

   Log* log = new Log(TestPrinter);
 
   EXPECT_EQ(reinterpret_cast<const char*>(NULL), test_output_);
   log->Print("Hello %s", "World");
   EXPECT_STREQ("Hello World", test_output_);
+
+  delete log;
+  LogTestHelper::FreeTestOutput();
 }
 
 
 TEST_CASE(Log_Block) {
   test_output_ = NULL;
   Log* log = new Log(TestPrinter);
 
   EXPECT_EQ(reinterpret_cast<const char*>(NULL), test_output_);
   {
     LogBlock ba(thread, log);
     log->Print("APPLE");
     EXPECT_EQ(reinterpret_cast<const char*>(NULL), test_output_);
     {
       LogBlock ba(thread, log);
       log->Print("BANANA");
       EXPECT_EQ(reinterpret_cast<const char*>(NULL), test_output_);
     }
     EXPECT_STREQ("BANANA", test_output_);
   }
   EXPECT_STREQ("APPLE", test_output_);
+  delete log;
+  LogTestHelper::FreeTestOutput();
 }
 
 }  // namespace dart