add more tests and update based on comments

pkg/kn/commands/source/apiserver/flags.go

@@ -47,7 +47,7 @@ type resourceSpec struct {
 	IsController bool
 }
 
-// getAPIServerResourceArray is to return an array of ApiServerResource from a string. A sample is Event:v1:true,Pod:v2:false
+// getAPIServerResourceArray is to construct an array of resources.
 func (f *APIServerSourceUpdateFlags) getAPIServerResourceArray() ([]resourceSpec, error) {
 	var resourceList []resourceSpec
 	for _, r := range f.Resources {
@@ -60,7 +60,7 @@ func (f *APIServerSourceUpdateFlags) getAPIServerResourceArray() ([]resourceSpec
 	return resourceList, nil
 }
 
-// getAPIServerResourceArray is to return an array of ApiServerResource from a string. A sample is Event:v1:true
+// getUpdateAPIServerResourceArray is to construct an array of resources for update action.
 func (f *APIServerSourceUpdateFlags) getUpdateAPIServerResourceArray() ([]resourceSpec, []resourceSpec, error) {
 	var added []resourceSpec
 	var removed []resourceSpec
@@ -83,6 +83,7 @@ func (f *APIServerSourceUpdateFlags) getUpdateAPIServerResourceArray() ([]resour
 	return added, removed, nil
 }
 
+//getValidResource is to parse resource spec from a string
 func getValidResource(resource string) (*resourceSpec, error) {
 	var isController = false //false as default
 	var err error