Use createEditorAndMakeActive and call editorBeingDeleted on teardown

createEditor() is now private in JUCE 8. createEditorAndMakeActive() registers
the editor with the processor, so the host must call editorBeingDeleted() before
destruction to clear activeEditor and avoid the dtor jassert.

Author: sudara

Source/TestUtilities.h

@@ -145,7 +145,7 @@ static std::unique_ptr<juce::AudioProcessorEditor> createAndShowEditorOnMessageT
             return {};
 
         jassert (instance.getActiveEditor() == nullptr);
-        editor.reset (instance.createEditor());
+        editor.reset (instance.createEditorAndMakeActive());
 
         if (editor)
         {
@@ -175,16 +175,25 @@ static std::unique_ptr<juce::AudioProcessorEditor> createAndShowEditorOnMessageT
 
 static void deleteEditorOnMessageThread (std::unique_ptr<juce::AudioProcessorEditor> editor)
 {
-    if (juce::MessageManager::getInstance()->isThisTheMessageThread())
+    auto destroy = [&editor]
     {
+        // createEditorAndMakeActive() registers the editor with the processor;
+        // the host (us) is responsible for calling editorBeingDeleted() before destruction.
+        if (editor != nullptr)
+            editor->processor.editorBeingDeleted (editor.get());
         editor.reset();
+    };
+
+    if (juce::MessageManager::getInstance()->isThisTheMessageThread())
+    {
+        destroy();
         return;
     }
 
     juce::WaitableEvent waiter;
     juce::MessageManager::callAsync ([&]
                                {
-                                   editor.reset();
+                                   destroy();
                                    waiter.signal();
                                });
     waiter.wait();