Teacher education or Testing learners ?

Hello,
Can you, please help me just by explaining this theme ?
“Assessment and testing in English Language Education”
What I know is that the underlined sentence means Teacher training, so ; does the whole theme mean testing teacher’s training or testing and assessing foreign language learners?
And we have to tackle this theme, will I have to cutter “teacher education” or only testing learners?
I will be really thankful if you can explain to me.

Without you telling me what the underlined part referred to, I would have assumed it included learners, so it's unclear to me.

Ok, does the role of testing means the purposes of testing, the same?
and does the principals of testing means its features?

The role is the part it plays- is it the only/main form of assessment, etc. The principles would be the underlying ideas behind the tests.

thank you for the clarification.