Add unit test for HpackDynamicTable. (netty#10389)

Motivation:

`HpackDynamicTable` needs some test cases to ensure bug-free.

Modification:

Add unit test for `HpackDynamicTable`.

Result:

Improve test coverage slightly.

codec-http2/src/test/java/io/netty/handler/codec/http2/HpackDynamicTableTest.java

@@ -0,0 +1,106 @@
+/*
+ * Copyright 2020 The Netty Project
+ *
+ * The Netty Project licenses this file to you 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 io.netty.handler.codec.http2;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.fail;
+
+import org.junit.Test;
+
+public class HpackDynamicTableTest {
+
+    @Test
+    public void testLength() {
+        HpackDynamicTable table = new HpackDynamicTable(100);
+        assertEquals(0, table.length());
+        HpackHeaderField entry = new HpackHeaderField("foo", "bar");
+        table.add(entry);
+        assertEquals(1, table.length());
+        table.clear();
+        assertEquals(0, table.length());
+    }
+
+    @Test
+    public void testSize() {
+        HpackDynamicTable table = new HpackDynamicTable(100);
+        assertEquals(0, table.size());
+        HpackHeaderField entry = new HpackHeaderField("foo", "bar");
+        table.add(entry);
+        assertEquals(entry.size(), table.size());
+        table.clear();
+        assertEquals(0, table.size());
+    }
+
+    @Test
+    public void testGetEntry() {
+        HpackDynamicTable table = new HpackDynamicTable(100);
+        HpackHeaderField entry = new HpackHeaderField("foo", "bar");
+        table.add(entry);
+        assertEquals(entry, table.getEntry(1));
+        table.clear();
+        try {
+            table.getEntry(1);
+            fail();
+        } catch (IndexOutOfBoundsException e) {
+            //success
+        }
+    }
+
+    @Test(expected = IndexOutOfBoundsException.class)
+    public void testGetEntryExceptionally() {
+        HpackDynamicTable table = new HpackDynamicTable(1);
+        table.getEntry(1);
+    }
+
+    @Test
+    public void testRemove() {
+        HpackDynamicTable table = new HpackDynamicTable(100);
+        assertNull(table.remove());
+        HpackHeaderField entry1 = new HpackHeaderField("foo", "bar");
+        HpackHeaderField entry2 = new HpackHeaderField("hello", "world");
+        table.add(entry1);
+        table.add(entry2);
+        assertEquals(entry1, table.remove());
+        assertEquals(entry2, table.getEntry(1));
+        assertEquals(1, table.length());
+        assertEquals(entry2.size(), table.size());
+    }
+
+    @Test
+    public void testSetCapacity() {
+        HpackHeaderField entry1 = new HpackHeaderField("foo", "bar");
+        HpackHeaderField entry2 = new HpackHeaderField("hello", "world");
+        final int size1 = entry1.size();
+        final int size2 = entry2.size();
+        HpackDynamicTable table = new HpackDynamicTable(size1 + size2);
+        table.add(entry1);
+        table.add(entry2);
+        assertEquals(2, table.length());
+        assertEquals(size1 + size2, table.size());
+        table.setCapacity((size1 + size2) * 2); //larger capacity
+        assertEquals(2, table.length());
+        assertEquals(size1 + size2, table.size());
+        table.setCapacity(size2); //smaller capacity
+        //entry1 will be removed
+        assertEquals(1, table.length());
+        assertEquals(size2, table.size());
+        assertEquals(entry2, table.getEntry(1));
+        table.setCapacity(0); //clear all
+        assertEquals(0, table.length());
+        assertEquals(0, table.size());
+    }
+}