I could test you could test he could test we could test you could test they could test
V-ing form
I could be testing you could be testing he could be testing we could be testing you could be testing they could be testing
Perfect
I could have tested you could have tested he could have tested we could have tested you could have tested they could have tested
V-ing perfect
I could have been testing you could have been testing he could have been testing we could have been testing you could have been testing they could have been testing
Negation
Simple form
I could not test you could not test he could not test we could not test you could not test they could not test
V-ing form
I could not be testing you could not be testing he could not be testing we could not be testing you could not be testing they could not be testing
Perfect
I could not have tested you could not have tested he could not have tested we could not have tested you could not have tested they could not have tested
V-ing perfect
I could not have been testing you could not have been testing he could not have been testing we could not have been testing you could not have been testing they could not have been testing
Interrogative form
Simple form
could I test? could you test? could he test? could we test? could you test? could they test?
V-ing form
could I be testing? could you be testing? could he be testing? could we be testing? could you be testing? could they be testing?
Perfect
could I have tested? could you have tested? could he have tested? could we have tested? could you have tested? could they have tested?
V-ing perfect
could I have been testing? could you have been testing? could he have been testing? could we have been testing? could you have been testing? could they have been testing?
Interro-negative form
Simple form
could I not test? could you not test? could he not test? could we not test? could you not test? could they not test?
V-ing form
could I not be testing? could you not be testing? could he not be testing? could we not be testing? could you not be testing? could they not be testing?
Perfect
could I not have tested? could you not have tested? could he not have tested? could we not have tested? could you not have tested? could they not have tested?
V-ing perfect
could I not have been testing? could you not have been testing? could he not have been testing? could we not have been testing? could you not have been testing? could they not have been testing?