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 couldn't test you couldn't test he couldn't test we couldn't test you couldn't test they couldn't test
V-ing form
I couldn't be testing you couldn't be testing he couldn't be testing we couldn't be testing you couldn't be testing they couldn't be testing
Perfect
I couldn't have tested you couldn't have tested he couldn't have tested we couldn't have tested you couldn't have tested they couldn't have tested
V-ing perfect
I couldn't have been testing you couldn't have been testing he couldn't have been testing we couldn't have been testing you couldn't have been testing they couldn't 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
couldn't I test? couldn't you test? couldn't he test? couldn't we test? couldn't you test? couldn't they test?
V-ing form
couldn't I be testing? couldn't you be testing? couldn't he be testing? couldn't we be testing? couldn't you be testing? couldn't they be testing?
Perfect
couldn't I have tested? couldn't you have tested? couldn't he have tested? couldn't we have tested? couldn't you have tested? couldn't they have tested?
V-ing perfect
couldn't I have been testing? couldn't you have been testing? couldn't he have been testing? couldn't we have been testing? couldn't you have been testing? couldn't they have been testing?