Send what listeners print at start-up in the worker's greeting

Listeners that print while they are created raced with the first test:
the text went through the worker's error stream and could reach the
runner after it had given the worker a test, which then claimed it as its
own output. The worker now captures Catch2's standard streams while it
creates the listeners and starts the run, sends the text in its hello
message, and the runner writes it to its standard error.

Catch2's stream redirect now remembers the buffer to restore when a
redirect starts rather than when it is made, so a stream whose buffer
changed in between is restored to the right one.

1 files changed, 14 insertions, 3 deletions

diff --git a/src/Progmasoft/Runner/Execution.cpp b/src/Progmasoft/Runner/Execution.cpp
index 77a4771a..3a2206d0 100644
--- a/src/Progmasoft/Runner/Execution.cpp
+++ b/src/Progmasoft/Runner/Execution.cpp
@@ -10,6 +10,7 @@
 #include <catch2/internal/catch_context.hpp>
 #include <catch2/internal/catch_reporter_registry.hpp>
 #include <catch2/internal/catch_run_context.hpp>
+#include <catch2/internal/catch_stdstreams.hpp>
 #include <catch2/internal/catch_string_manip.hpp>
 #include <catch2/reporters/catch_reporter_multi.hpp>
 #include <chrono>
@@ -17,6 +18,7 @@
 #include <cstdlib>
 #include <mutex>
 #include <optional>
+#include <sstream>
 
 #include "Execution.hpp"
 #include "Process.hpp"
@@ -543,14 +545,23 @@ namespace Progmasoft::Catch3::Runner
                 connected = false;
             }
         };
-        // Listeners are created and told of the run before the greeting, so
-        // what they print then is written before the runner assigns a test
-        // and is not mistaken for that test's output.
+        // Listeners are created, and told of the run, before the greeting.
+        // What they print then travels in the greeting: through the error
+        // stream it could arrive after the runner gave this worker a test,
+        // and pass for that test's output.
+        std::ostringstream startup;
+        auto *const previousOut = Catch::cout().rdbuf(startup.rdbuf());
+        auto *const previousErr = Catch::cerr().rdbuf(startup.rdbuf());
+        auto *const previousLog = Catch::clog().rdbuf(startup.rdbuf());
         TestExecutor executor{ options, *catalog, programName, send };
+        Catch::cout().rdbuf(previousOut);
+        Catch::cerr().rdbuf(previousErr);
+        Catch::clog().rdbuf(previousLog);
         std::fflush(stdout);
         std::fflush(stderr);
 
         JsonValue hello = Message("hello");
+        hello.Set("output", startup.str());
         hello.Set("pid", CurrentProcessId());
         hello.Set("identity", catalog->Identity());
         hello.Set("tests", catalog->Tests().size());