I could retest you could retest he could retest we could retest you could retest they could retest
V-ing form
I could be retesting you could be retesting he could be retesting we could be retesting you could be retesting they could be retesting
Perfect
I could have retested you could have retested he could have retested we could have retested you could have retested they could have retested
V-ing perfect
I could have been retesting you could have been retesting he could have been retesting we could have been retesting you could have been retesting they could have been retesting
Negation
Simple form
I couldn't retest you couldn't retest he couldn't retest we couldn't retest you couldn't retest they couldn't retest
V-ing form
I couldn't be retesting you couldn't be retesting he couldn't be retesting we couldn't be retesting you couldn't be retesting they couldn't be retesting
Perfect
I couldn't have retested you couldn't have retested he couldn't have retested we couldn't have retested you couldn't have retested they couldn't have retested
V-ing perfect
I couldn't have been retesting you couldn't have been retesting he couldn't have been retesting we couldn't have been retesting you couldn't have been retesting they couldn't have been retesting
Interrogative form
Simple form
could I retest? could you retest? could he retest? could we retest? could you retest? could they retest?
V-ing form
could I be retesting? could you be retesting? could he be retesting? could we be retesting? could you be retesting? could they be retesting?
Perfect
could I have retested? could you have retested? could he have retested? could we have retested? could you have retested? could they have retested?
V-ing perfect
could I have been retesting? could you have been retesting? could he have been retesting? could we have been retesting? could you have been retesting? could they have been retesting?
Interro-negative form
Simple form
couldn't I retest? couldn't you retest? couldn't he retest? couldn't we retest? couldn't you retest? couldn't they retest?
V-ing form
couldn't I be retesting? couldn't you be retesting? couldn't he be retesting? couldn't we be retesting? couldn't you be retesting? couldn't they be retesting?
Perfect
couldn't I have retested? couldn't you have retested? couldn't he have retested? couldn't we have retested? couldn't you have retested? couldn't they have retested?
V-ing perfect
couldn't I have been retesting? couldn't you have been retesting? couldn't he have been retesting? couldn't we have been retesting? couldn't you have been retesting? couldn't they have been retesting?