Send mail when the Execution Status changed

hi Experts.
In this moment, I need to send mail when the "execution status" has changed,
the code for send the mail this works fine, but the problem is why I not found the event where I placed the code.

I have these posibilities:
Test_FieldCanChange
l TestConfiguration_FieldCanChange
l TestFolder_FieldCanChange
l TestSet_FieldCanChange
l TestSetFolder_FieldCanChange
l TestSetTests_FieldCanChange

but I don´t know where place the code.

The identity that I use is: test
but also I have these posibilities:
TestSet --- Test set data
TestSetTests --- Test instance data

the label is: "TS_EXEC_STATUS"

I attached the image.

I hope you can help me.

Regards