pw_multisink: Fix compiler warnings for tests

GCC warns about constructing a MultiBuf with an uninitialized array, so
initialize it first. This isn't a problem in practice because the
uninitialized data is never read.

Also, ensure the test builds when joining is disabled, though none of
the tests can run.

Bug: b/343480404
Change-Id: I24a0157228621cae7ed85562929f65a663d7fc82
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/212051
Lint: Lint 🤖 <[email protected]>
Pigweed-Auto-Submit: Wyatt Hepler <[email protected]>
Presubmit-Verified: CQ Bot Account <[email protected]>
Reviewed-by: Anthony DiGirolamo <[email protected]>
Commit-Queue: Wyatt Hepler <[email protected]>

pw_multisink/multisink_threaded_test.cc

@@ -26,21 +26,24 @@
 
 namespace pw::multisink {
 namespace {
+
 constexpr size_t kEntryBufferSize = sizeof("message 000");
 constexpr size_t kMaxMessageCount = 250;
 constexpr size_t kBufferSize = kMaxMessageCount * kEntryBufferSize;
 
 using MessageSpan = span<const StringBuffer<kEntryBufferSize>>;
 
-void CompareSentAndReceivedMessages(const MessageSpan& sent_messages,
-                                    const MessageSpan& received_messages) {
+// This function is unused if joining is not supported.
+[[maybe_unused]] void CompareSentAndReceivedMessages(
+    const MessageSpan& sent_messages, const MessageSpan& received_messages) {
   ASSERT_EQ(sent_messages.size(), received_messages.size());
   for (size_t i = 0; i < sent_messages.size(); ++i) {
     ASSERT_EQ(sent_messages[i].size(), received_messages[i].size());
     EXPECT_EQ(std::string_view(sent_messages[i]),
               std::string_view(received_messages[i]));
   }
 }
+
 }  // namespace
 
 // Static message pool to avoid recreating messages for every test and avoids
@@ -183,14 +186,14 @@ class LogWriterThread : public thread::ThreadCore {
 
 class MultiSinkTest : public ::testing::Test {
  protected:
-  MultiSinkTest() : multisink_(buffer_) {}
+  MultiSinkTest() : buffer_{}, multisink_(buffer_) {}
 
   std::byte buffer_[kBufferSize];
   MultiSink multisink_;
-
- private:
 };
 
+#if PW_THREAD_JOINING_ENABLED
+
 TEST_F(MultiSinkTest, SingleWriterSingleReader) {
   const uint32_t log_count = 100;
   const uint32_t drop_count = 5;
@@ -368,4 +371,6 @@ TEST_F(MultiSinkTest, OverflowMultisink) {
   // can't control the order threads will operate.
 }
 
+#endif  // PW_THREAD_JOINING_ENABLED
+
 }  // namespace pw::multisink