Create unit test for LazilyInstantiate

spring-cloud-kubernetes-core/src/main/java/org/springframework/cloud/kubernetes/LazilyInstantiate.java

@@ -29,7 +29,7 @@ public class LazilyInstantiate<T> implements Supplier<T> {
         return current.get();
     }
 
-    private LazilyInstantiate(Supplier supplier) {
+    private LazilyInstantiate(Supplier<T> supplier) {
         this.supplier = supplier;
         this.current = () -> swapper();
     }

spring-cloud-kubernetes-core/src/test/java/org/springframework/cloud/kubernetes/LazilyInstantiateTest.java

@@ -0,0 +1,72 @@
+/*
+ *     Copyright (C) 2016 to the original authors.
+ *
+ *     Licensed under the Apache License, Version 2.0 (the "License");
+ *     you may not use this file except in compliance with the License.
+ *     You may obtain a copy of the License at
+ *
+ *             http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *     Unless required by applicable law or agreed to in writing, software
+ *     distributed under the License is distributed on an "AS IS" BASIS,
+ *     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *     See the License for the specific language governing permissions and
+ *     limitations under the License.
+ */
+
+package org.springframework.cloud.kubernetes;
+
+import static org.junit.Assert.assertEquals;
+import static org.mockito.Mockito.verifyZeroInteractions;
+import static org.mockito.Mockito.when;
+
+import java.util.function.Supplier;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.runners.MockitoJUnitRunner;
+
+@RunWith(MockitoJUnitRunner.class)
+public class LazilyInstantiateTest {
+
+	private static final String SINGLETON = "singleton";
+
+	@Mock
+	private Supplier<String> mockSupplier;
+
+	@Before
+	public void setUp() throws Exception {
+		// common setup
+		when(mockSupplier.get()).thenReturn(SINGLETON)
+				.thenThrow(new RuntimeException("Supplier was called more than once!"));
+	}
+
+	@Test
+	public void supplierNotCalledInLazyInstantiateFactoryMethod() {
+		LazilyInstantiate.using(mockSupplier);
+
+		// verify
+		verifyZeroInteractions(mockSupplier);
+	}
+
+	@Test
+	public void factoryReturnsSingletonFromSupplier() {
+		LazilyInstantiate<String> lazyStringFactory = LazilyInstantiate.using(mockSupplier);
+		String singletonString = lazyStringFactory.get();
+
+		// verify
+		assertEquals(SINGLETON, singletonString);
+	}
+
+	@Test
+	public void factoryOnlyCallsSupplierOnce() {
+		LazilyInstantiate<String> lazyStringFactory = LazilyInstantiate.using(mockSupplier);
+		lazyStringFactory.get();
+
+		// mock will throw exception if it is called more than once
+		lazyStringFactory.get();
+	}
+
+}