diff --git a/cmd/kubeadm/app/apis/kubeadm/validation/validation_test.go b/cmd/kubeadm/app/apis/kubeadm/validation/validation_test.go
new file mode 100644
index 00000000000..5ea16980bb4
--- /dev/null
+++ b/cmd/kubeadm/app/apis/kubeadm/validation/validation_test.go
@@ -0,0 +1,31 @@
+package validation
+
+import (
+	"testing"
+
+	"k8s.io/apimachinery/pkg/util/validation/field"
+)
+
+func TestValidateServiceSubnet(t *testing.T) {
+	var tests = []struct {
+		s        string
+		f        *field.Path
+		expected bool
+	}{
+		{"", nil, false},
+		{"this is not a cidr", nil, false}, // not a CIDR
+		{"10.0.0.1", nil, false},           // not a CIDR
+		{"192.0.2.0/1", nil, false},        // CIDR too smal
+		{"192.0.2.0/24", nil, true},
+	}
+	for _, rt := range tests {
+		actual := ValidateServiceSubnet(rt.s, rt.f)
+		if (len(actual) == 0) != rt.expected {
+			t.Errorf(
+				"failed ValidateServiceSubnet:\n\texpected: %t\n\t  actual: %t",
+				rt.expected,
+				(len(actual) == 0),
+			)
+		}
+	}
+}