Post exit code from unit tests when asyncify=on

- with asyncify, the python server always got an exit code of `1`
  because `main` implicitly returned 1.
- as a result, exit code is specially handled so that `ctest` can decide whether the test failed or passed.

CMake/vtkTestingDriver.cmake

@@ -9,4 +9,15 @@ SET(CMAKE_TESTDRIVER_BEFORE_TESTMAIN
   vtkLogger::Init(ac, av);
 ")
 
-SET(CMAKE_TESTDRIVER_AFTER_TESTMAIN "")
+SET(CMAKE_TESTDRIVER_AFTER_TESTMAIN
+"
+#if defined(__EMSCRIPTEN__)
+  // When asyncify is used, emscripten sets up the wasm module 
+  // such that the `main` function always returns 1.
+  // Explicitly post the test's exit code back to the server.
+  if (emscripten_has_asyncify())
+  {
+    vtkEmscriptenTestUtilities::PostExitCode(result);
+  }
+#endif
+")

Testing/Core/vtkEmscriptenTestUtilities.cxx

@@ -89,5 +89,10 @@ void vtkEmscriptenTestUtilities::DumpFile(
   const auto* bytes = reinterpret_cast<const uint8_t*>(data);
   vtkDumpFile(hostFilePath.c_str(), bytes, n);
 }
+
+void vtkEmscriptenTestUtilities::PostExitCode(int code)
+{
+  vtkPostExitCode(code);
+}
 VTK_ABI_NAMESPACE_END
 #endif // __EMSCRIPTEN__

Testing/Core/vtkEmscriptenTestUtilities.h

@@ -10,6 +10,8 @@
 #include <cstdint>                // for uint8_t
 #include <string>                 // for string
 
+#include <emscripten/emscripten.h> // for emscripten_ API
+
 VTK_ABI_NAMESPACE_BEGIN
 
 class VTKTESTINGCORE_EXPORT vtkEmscriptenTestUtilities
@@ -24,12 +26,16 @@ public:
     const std::string& hostFilePath, const std::string& sandboxedFilePath);
   static std::string PreloadDataFile(const std::string& hostFilePath);
   static void DumpFile(const std::string& hostFilePath, const void* data, std::size_t n);
+  static void PostExitCode(int code);
 };
 
+// These functions are implemented externally in javascript.
+// The static methods of vtkEmscriptenTestUtilities call into these methods.
 extern "C"
 {
   void* vtkPreloadDataFileIntoMemory(const char* hostFilePath);
   void vtkDumpFile(const char* hostFilePath, const uint8_t* data, size_t nbytes);
+  void vtkPostExitCode(int code);
 }
 
 VTK_ABI_NAMESPACE_END

Testing/Core/vtkEmscriptenTestUtilities.js

@@ -55,6 +55,15 @@ var vtkEmscriptenTestUtilities = {
     const byteArray = HEAPU8.subarray(data, data + nbytes);
     req.send(new Uint8Array(byteArray));
   },
+
+  /**
+   * Send the exit code to the server.
+   */
+  vtkPostExitCode__sig: "vi",
+  vtkPostExitCode: (code) => {
+    // this function is defined in Testing/WebAssembly/templates/index.html
+    finalize(code)
+  },
 };
 
 mergeInto(LibraryManager.library, vtkEmscriptenTestUtilities);

Testing/Core/vtkTestDriver.h

@@ -14,7 +14,8 @@
 
 #include <vtkLogger.h> // for logging
 
-#include "vtkWindowsTestUtilities.h" // for windows stack trace
+#include "vtkEmscriptenTestUtilities.h" // for wasm I/O and exit helper
+#include "vtkWindowsTestUtilities.h"    // for windows stack trace
 
 #endif
 // VTK-HeaderTest-Exclude: vtkTestDriver.h