Add unit tests for EmptyDiscreteResources

Change-Id: I2dd53e98eb3129607f5faadf3a1f9ecab378d36c

+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * 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.onosproject.store.resource.impl;
+
+import com.google.common.collect.ImmutableSet;
+import org.junit.Test;
+import org.onosproject.net.DeviceId;
+import org.onosproject.net.resource.DiscreteResource;
+import org.onosproject.net.resource.Resources;
+
+import java.util.Optional;
+
+import static org.hamcrest.Matchers.is;
+import static org.junit.Assert.*;
+
+public class EmptyDiscreteResourcesTest {
+    private EmptyDiscreteResources sut = EmptyDiscreteResources.INSTANCE;
+
+    @Test
+    public void testLookup() {
+        assertThat(sut.lookup(Resources.discrete(DeviceId.deviceId("a")).id()), is(Optional.empty()));
+    }
+
+    @Test
+    public void testDifference() {
+        DiscreteResource res1 = Resources.discrete(DeviceId.deviceId("a")).resource();
+        DiscreteResource res2 = Resources.discrete(DeviceId.deviceId("b")).resource();
+
+        assertThat(sut.difference(DiscreteResources.of(ImmutableSet.of(res1))),
+                is(EmptyDiscreteResources.INSTANCE));
+        assertThat(sut.difference(DiscreteResources.of(ImmutableSet.of(res2))),
+                is(EmptyDiscreteResources.INSTANCE));
+    }
+
+    @Test
+    public void testIsEmpty() {
+        assertThat(sut.isEmpty(), is(true));
+    }
+
+    @Test
+    public void testContainsAny() {
+        DiscreteResource res1 = Resources.discrete(DeviceId.deviceId("a")).resource();
+        DiscreteResource res2 = Resources.discrete(DeviceId.deviceId("b")).resource();
+
+        assertThat(sut.containsAny(ImmutableSet.of(res1)), is(false));
+        assertThat(sut.containsAny(ImmutableSet.of(res2)), is(false));
+    }
+
+    @Test
+    public void testAdd() {
+        DiscreteResource res1 = Resources.discrete(DeviceId.deviceId("a")).resource();
+        DiscreteResource res2 = Resources.discrete(DeviceId.deviceId("b")).resource();
+
+        assertThat(sut.add(DiscreteResources.of(ImmutableSet.of(res1))),
+                is(DiscreteResources.of(ImmutableSet.of(res1))));
+        assertThat(sut.add(DiscreteResources.of(ImmutableSet.of(res2))),
+                is(DiscreteResources.of(ImmutableSet.of(res2))));
+    }
+
+    @Test
+    public void testValues() {
+        assertThat(sut.values(), is(ImmutableSet.of()));
+    }
+}