Flesh out fillOrder integration tests

contracts/integrations/test/actors/index.ts

@@ -2,5 +2,8 @@ export { Actor } from './base';
 export { Maker } from './maker';
 export { PoolOperator } from './pool_operator';
 export { FeeRecipient } from './fee_recipient';
+export { Staker } from './staker';
+export { Keeper } from './keeper';
+export { Taker } from './taker';
 export * from './hybrids';
 export * from './utils';