[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 #573

Job	Run time
unpack-envvars	3s
Docker Build Images (datacatalog) / build_docker	3m 31s
Docker Build Images (flyteadmin) / build_docker	3m 1s
Docker Build Images (flytecopilot) / build_docker	4m 6s
Docker Build Images (flytepropeller) / build_docker	3m 28s
Build Images / Build & Push Image (datacatalog) / Push to Github Registry	2m 12s
Build Images / Build & Push Image (flyteadmin) / Push to Github Registry	5m 31s
Build Images / Build & Push Image (flytecopilot) / Push to Github Registry	4m 32s
Build Images / Build & Push Image (flytepropeller) / Push to Github Registry	7m 12s
Build Images / Build & Push Image (flytescheduler) / Push to Github Registry	3m 42s
Check Go Generate (datacatalog) / Go Generate	2m 5s
Check Go Generate (flytecopilot) / Go Generate	1m 30s
Check Go Generate (flytepropeller) / Go Generate	3m 56s
Check Go Generate (flyteadmin) / Go Generate	3m 47s
Lint (flyteidl) / Run Lint	2m 48s
Lint (datacatalog) / Run Lint	3m 57s
Lint (flyteadmin) / Run Lint	3m 44s
Lint (flytepropeller) / Run Lint	3m 34s
Lint (flyteplugins) / Run Lint	5m 28s
Lint (flytestdlib) / Run Lint	3m 21s
Unit Tests (datacatalog) / Run Unit Test	2m 7s
Unit Tests (flyteadmin) / Run Unit Test	3m 47s
Unit Tests (flyteplugins) / Run Unit Test	3m 38s
Unit Tests (flytepropeller) / Run Unit Test	3m 55s
Unit Tests (flytecopilot) / Run Unit Test	2m 26s
Unit Tests (flytestdlib) / Run Unit Test	2m 42s
Integration Test (flyteadmin) / Integration tests	8m 0s
	1h 38m 3s

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