Added func ValidateZone

The zone parameter provided in a Storage Class may erroneously be an empty string or contain only spaces and tab characters. Such situation shall be detected and reported as an error.

That's why the func ValidateZone was added.

pkg/volume/util.go

@@ -424,3 +424,13 @@ func ZonesToSet(zonesString string) (sets.String, error) {
 	}
 	return zonesSet, nil
 }
+
+// ValidateZone returns:
+// - an error in case zone is an empty string or contains only any combination of spaces and tab characters
+// - nil otherwise
+func ValidateZone(zone string) error {
+	if strings.TrimSpace(zone) == "" {
+		return fmt.Errorf("the provided %q zone is not valid, it's an empty string or contains only spaces and tab characters", zone)
+	}
+	return nil
+}

pkg/volume/util_test.go

@@ -557,3 +557,23 @@ func TestZonesToSet(t *testing.T) {
 		}
 	}
 }
+
+func TestValidateZone(t *testing.T) {
+	functionUnderTest := "ValidateZone"
+
+	// First part: want an error
+	errCases := []string{"", " 	 	 "}
+	for _, errCase := range errCases {
+		if got := ValidateZone(errCase); got == nil {
+			t.Errorf("%v(%v) returned (%v), want (%v)", functionUnderTest, errCase, got, "an error")
+		}
+	}
+
+	// Second part: want no error
+	succCases := []string{" us-east-1a	"}
+	for _, succCase := range succCases {
+		if got := ValidateZone(succCase); got != nil {
+			t.Errorf("%v(%v) returned (%v), want (%v)", functionUnderTest, succCase, got, nil)
+		}
+	}
+}