[flytepropeller] Add Tests in v1alpha.go including array_test.go, branch_test.go, error_test.go, and iface_test.go with 0.13% Coverage Improvment

[flytepropeller] Add Tests in v1alpha.go including array_test.go, branch_test.go, error_test.go, and iface_test.go with 0.13% Coverage Improvment #429