Fix checkstyle.

spring-cloud-openfeign-core/src/test/java/org/springframework/cloud/openfeign/encoding/Invoices.java

@@ -30,6 +30,10 @@ import org.springframework.cloud.openfeign.encoding.app.domain.Invoice;
  */
 final class Invoices {
 
+	private Invoices() {
+		throw new IllegalStateException("Should not instantiate utility class");
+	}
+
 	public static List<Invoice> createInvoiceList(int count) {
 		final List<Invoice> invoices = new ArrayList<>();
 		for (int ind = 0; ind < count; ind++) {

spring-cloud-openfeign-core/src/test/java/org/springframework/cloud/openfeign/test/EqualsAndHashCodeAssert.java

@@ -25,7 +25,11 @@ import static org.assertj.core.api.Assertions.assertThat;
  *
  * @author Jonatan Ivanov
  */
-public class EqualsAndHashCodeAssert {
+public final class EqualsAndHashCodeAssert {
+
+	private EqualsAndHashCodeAssert() {
+		throw new IllegalStateException("Should not instantiate utility class");
+	}
 
 	/**
 	 * Checks if equals is reflexive: for any non-null reference value x, x.equals(x)