Most of the same tools required for Knative Serving development are required for the operator, too.
You'll probably need to install Istio. For the e2e tests to pass, you only need its CRD's.
You should clone this repo to $GOPATH/src/knative.dev/operator. All commands
below are relative to that path.
To install the operator:
ko apply -f config/
To run the unit tests:
go test -v ./...
To run the e2e tests:
ko apply -f config/
kubectl create namespace knative-serving
kubectl create namespace knative-eventing
go test -v -tags=e2e -count=1 ./test/e2e