message: test: Improve "invalid_command" subtest in system_tests for Windows
  No need to explain code with comments.
diff: @@ -28,15 +28,6 @@ BOOST_AUTO_TEST_CASE(dummy)
  #ifdef ENABLE_EXTERNAL_SIGNER
  -bool checkMessage(const std::runtime_error& ex)
  -{
  - // On Linux & Mac: "No such file or directory"
  - // On Windows: "The system cannot find the file specified."
  - const std::string what(ex.what());
  - BOOST_CHECK(what.find("file") != std::string::npos);
  - return true;
  -}
  -
  BOOST_AUTO_TEST_CASE(run_command)
  {
  {
  @@ -56,7 +47,17 @@ BOOST_AUTO_TEST_CASE(run_command)
  }
  {
  // An invalid command is handled by Boost
  - BOOST_CHECK_EXCEPTION(RunCommandParseJSON("invalid_command"), boost::process::process_error, checkMessage); // Command failed
  +#ifdef WIN32
  + const std::string expected{"The system cannot find the file specified."};
  +#else
  + const std::string expected{"No such file or directory"};
  +#endif
  + BOOST_CHECK_EXCEPTION(RunCommandParseJSON("invalid_command"), boost::process::process_error, [&](const boost::process::process_error& e) {
  + const std::string what(e.what());
  + BOOST_CHECK(what.find("RunCommandParseJSON error:") == std::string::npos);
  + BOOST_CHECK(what.find(expected) != std::string::npos);
  + return true;
  + });
  }
  {
  // Return non-zero exit code, no output to stderr
  