Allow to specify target cluster architecture for tests

When e2e or examples tests are started, hardware architectutere of the host
is always used. However test cases can be exectuted on cluster with another architecture,
using `--kubeconfig` parameter.
`TEST_RUNTIME_ARCH` allows to specify target cluster architecture to be able to use
correct restrictions and modifications, specific to concrete arch.

Signed-off-by: Yulia Gaponenko <yulia.gaponenko1@de.ibm.com>

test/README.md

@@ -156,6 +156,10 @@ go test -v -count=1 -tags=e2e -timeout=20m ./test
 go test -v -count=1 -tags=e2e -timeout=20m ./test --kubeconfig ~/special/kubeconfig --cluster myspecialcluster
 ```
 
+If tests are applied to the cluster with hardware architecture different to the base one
+(for instance `go test` starts on amd64 architecture and `--kubeconfig` points to s390x Kubernetes cluster),
+use `TEST_RUNTIME_ARCH` environment variable to specify the target hardware architecture(amd64, s390x, ppc64le, arm, arm64, etc)
+
 You can also use
 [all of flags defined in `knative/pkg/test`](https://github.com/knative/pkg/tree/master/test#flags).
 

test/multiarch_utils.go

@@ -17,6 +17,7 @@ limitations under the License.
 package test
 
 import (
+	"os"
 	"runtime"
 	"testing"
 )
@@ -33,10 +34,20 @@ const (
 	Registry
 )
 
+// return architecture of the cluster where test suites will be executed.
+// default value is similar to build architecture, TEST_RUNTIME_ARCH is used when test target cluster has another architecture
+func getTestArch() string {
+	val, ok := os.LookupEnv("TEST_RUNTIME_ARCH")
+	if ok {
+		return val
+	}
+	return runtime.GOARCH
+}
+
 func initImageNames() map[int]string {
 	mapping := make(map[int]string)
 
-	switch arch := runtime.GOARCH; arch {
+	switch getTestArch() {
 	case "s390x":
 		mapping[BusyboxSha] = "busybox@sha256:4f47c01fa91355af2865ac10fef5bf6ec9c7f42ad2321377c21e844427972977"
 		mapping[Registry] = "ibmcom/registry:2.6.2.5"
@@ -51,7 +62,7 @@ func initImageNames() map[int]string {
 func initExcludedTests() map[string]bool {
 	mapping := make(map[string]bool)
 	tests := []string{}
-	switch arch := runtime.GOARCH; arch {
+	switch getTestArch() {
 	case "s390x":
 		//examples
 		tests = []string{
@@ -131,6 +142,6 @@ func GetTestImage(image int) string {
 // check if test name is in the excluded list and skip it
 func SkipIfExcluded(t *testing.T) {
 	if excludedTests[t.Name()] {
-		t.Skipf("skip for %s architecture", runtime.GOARCH)
+		t.Skipf("skip for %s architecture", getTestArch())
 	}
 }