Indicate vs Indicates

My question is whether indicate or indicates should be used in the following sentence:

The test ids ARB1 and ARB2 indicate(s) that two different samples were used, rather than representing different test methods.

My colleague is of the view that the subject "test ids ARB1 and ARB2" is plural, and hence the verb would be in it’s plural form (without an s) "indicate". I agree with him, but ultimately we’re unsure of ourselves hence the question here.