t Add unit testing to Godot using DocTest and added to GitHub Actions CI

Implements exit codes into the engine so tests can return their statuses.
Ideally we don't do this, and we use FIXUP logic to 'begin' and 'end' the engine execution for tests specifically.

Since realistically we're initialising the engine here we don't want to do that, since String should not require an engine startup to test a single header.

This lowers the complexity of running the unit tests and even for
physics should be possible to implement such a fix.

.github/workflows/linux_builds.yml

@@ -62,6 +62,11 @@ jobs:
         run: |
           scons -j2 verbose=yes warnings=all werror=yes platform=linuxbsd tools=yes target=release_debug module_mono_enabled=yes mono_glue=no
 
+      # Execute unit tests for the editor
+      - name: Unit Tests
+        run: |
+          ./bin/godot.linuxbsd.opt.tools.64.mono --test
+
   linux-template:
     runs-on: "ubuntu-20.04"
     name: Template w/ Mono (target=release, tools=no)

.github/workflows/macos_builds.yml

@@ -51,6 +51,11 @@ jobs:
         run: |
           scons -j2 verbose=yes warnings=all werror=yes platform=osx tools=yes target=release_debug
 
+      # Execute unit tests for the editor
+      - name: Unit Tests
+        run: |
+          ./bin/godot.osx.opt.tools.64 --test
+
   macos-template:
     runs-on: "macos-latest"
     name: Template (target=release, tools=no)

.github/workflows/windows_builds.yml

@@ -56,6 +56,11 @@ jobs:
       run: |
         scons -j2 verbose=yes warnings=all werror=yes platform=windows tools=yes target=release_debug
 
+    # Execute unit tests for the editor
+    - name: Unit Tests
+      run: |
+        ./bin/godot.windows.opt.tools.64.exe --test
+
 # Build Product Upload (tested and working)
 # sorry this is disabled until github can give us some more space as we would hit our limit very quickly
 # tested this code and it works fine so just enable it to get them back