WithSpan cleanups. (#210)

* Add WithSpanDeathTest.
* Remove unused ContextTestPeer.

Author: g-easy

opencensus/trace/internal/with_span_benchmark.cc

@@ -21,19 +21,9 @@
 #include "opencensus/trace/span.h"
 
 namespace opencensus {
-namespace context {
-class ContextTestPeer {
- public:
-  static const opencensus::trace::Span& CurrentSpan() {
-    return Context::InternalMutableCurrent()->span_;
-  }
-};
-}  // namespace context
 namespace trace {
 namespace {
 
-using opencensus::context::ContextTestPeer;
-
 void BM_WithSpanUnsampled(benchmark::State& state) {
   static ::opencensus::trace::NeverSampler sampler;
   auto span = Span::StartSpan("MySpan", /*parent=*/nullptr, {&sampler});

opencensus/trace/internal/with_span_test.cc

@@ -15,6 +15,7 @@
 #include "opencensus/trace/with_span.h"
 
 #include <iostream>
+#include <thread>
 
 #include "gtest/gtest.h"
 #include "opencensus/context/context.h"
@@ -106,4 +107,21 @@ TEST(WithSpanTest, DisabledViaConditional) {
   span1.End();
 }
 
+#ifndef NDEBUG
+TEST(WithSpanDeathTest, DestructorOnWrongThread) {
+  auto span = opencensus::trace::Span::StartSpan("MySpan");
+  EXPECT_DEATH_IF_SUPPORTED(
+      {
+        auto* ws = new opencensus::trace::WithSpan(span);
+        std::thread t([ws]() {
+          // Running the destructor in a different thread corrupts its
+          // thread-local Context. In debug mode, it assert()s.
+          delete ws;
+        });
+        t.join();
+      },
+      "must be destructed on the same thread");
+}
+#endif
+
 }  // namespace