gz_TEST: more output when tests fail (#479)

Signed-off-by: Steve Peters <[email protected]>

src/cmd/gz_TEST.cc

@@ -290,8 +290,8 @@ TEST(gzTest, TopicPublish)
         "-m", "gz.msgs.StringMsg",
         "-p", "data: \"good_value\""});
 
-    EXPECT_TRUE(output.cout.empty());
-    EXPECT_TRUE(output.cerr.empty());
+    EXPECT_TRUE(output.cout.empty()) << output.cout;
+    EXPECT_TRUE(output.cerr.empty()) << output.cerr;
     if (g_topicCBStr == "good_value")
       break;
     std::this_thread::sleep_for(std::chrono::milliseconds(60));
@@ -304,23 +304,26 @@ TEST(gzTest, TopicPublish)
     "-t", "/bar",
     "-m", "gz.msgs.__bad_msg_type",
     "-p", R"(data: "good_value")"});
-  EXPECT_EQ(output.cerr.compare(0, error.size(), error), 0);
+  EXPECT_EQ(output.cerr.compare(0, error.size(), error), 0)
+    << "error {" << error << "}, output.cerr {" << output.cerr << "}";
 
   // Try to publish using an incorrect topic name.
   error = "Topic [/] is not valid";
   output = custom_exec_str({"topic",
       "-t", "/",
       "-m", "gz.msgs.StringMsg",
       "-p", R"(data: "good_value")"});
-  EXPECT_EQ(output.cerr.compare(0, error.size(), error), 0);
+  EXPECT_EQ(output.cerr.compare(0, error.size(), error), 0)
+    << "error {" << error << "}, output.cerr {" << output.cerr << "}";
 
   // Try to publish using an incorrect number of arguments.
   error = "The following argument was not expected: wrong_topic";
   output = custom_exec_str({"topic",
       "-t", "/", "wrong_topic",
       "-m", "gz.msgs.StringMsg",
       "-p", R"(data: "good_value")"});
-  EXPECT_EQ(output.cerr.compare(0, error.size(), error), 0);
+  EXPECT_EQ(output.cerr.compare(0, error.size(), error), 0)
+    << "error {" << error << "}, output.cerr {" << output.cerr << "}";
 }
 
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