Unit tests for DefaultLoad class

Change-Id: I9f661bbb20199c190076bcf71537c6c881cebc3a

+/*
+ * Copyright 2015 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.net.statistic;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.containsString;
+import static org.hamcrest.Matchers.is;
+import static org.hamcrest.core.IsNot.not;
+
+/**
+ * Unit tests for DefaultLoad class.
+ */
+public class DefaultLoadTest {
+
+    @Before
+    public void reset() {
+        DefaultLoad.setPollInterval(10);
+    }
+
+    /**
+     * Tests the default constructor.
+     */
+    @Test
+    public void testDefaultConstructor() {
+        DefaultLoad load = new DefaultLoad();
+        assertThat(load.isValid(), is(false));
+        assertThat(load.latest(), is(-1L));
+        assertThat(load.rate(), is(0L));
+        assertThat(load.time(), is(not(0)));
+    }
+
+    /**
+     * Tests the current-previous constructor.
+     */
+    @Test
+    public void testCurrentPreviousConstructor() {
+        DefaultLoad load = new DefaultLoad(20, 10);
+        assertThat(load.isValid(), is(true));
+        assertThat(load.latest(), is(20L));
+        assertThat(load.rate(), is(1L));
+        assertThat(load.time(), is(not(0)));
+    }
+
+    /**
+     * Tests the current-previous-interval constructor.
+     */
+    @Test
+    public void testCurrentPreviousIntervalConstructor() {
+        DefaultLoad load = new DefaultLoad(20, 10, 1);
+        assertThat(load.isValid(), is(true));
+        assertThat(load.latest(), is(20L));
+        assertThat(load.rate(), is(10L));
+        assertThat(load.time(), is(not(0)));
+    }
+
+    /**
+     * Tests the toString operation.
+     */
+    @Test
+    public void testToString() {
+        DefaultLoad load = new DefaultLoad(20, 10);
+
+        String s = load.toString();
+        assertThat(s, containsString("Load{rate=1, latest=20}"));
+    }
+
+    /**
+     * Tests setting the poll interval.
+     */
+    @Test
+    public void testSettingPollInterval() {
+        DefaultLoad.setPollInterval(1);
+        DefaultLoad load = new DefaultLoad(40, 10);
+        assertThat(load.rate(), is(30L));
+    }
+}