Comma after introductory phrase? vs no error?? Help Please!!! Urgent!

Hello!
I am positive that there must be a comma after an introductory phrase that is a dependent clause. But on the SAT writing section, if the introductory phrase doesn’t have a comma, should i be sure that that would be the error? (as opposed to no error?)

What other comma/punctuation does the SAT test besides the comma splice?

Thanks!