Add Tests of BrotliDecoderChannel (#147)

Motivation:

Noticed there were no tests for BrotliDecoderChannel, so here are a few
for you to add.

Modification:

Created test cases for BrotliDecoderChannel.

Result:

See test cases

brotli4j/src/test/java/com/aayushatharva/brotli4j/decoder/BrotliDecoderChannelTest.java

@@ -0,0 +1,156 @@
+/*
+ *   Copyright (c) 2020-2023, Aayush Atharva
+ *
+ *   Brotli4j 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 com.aayushatharva.brotli4j.decoder;
+
+import com.aayushatharva.brotli4j.Brotli4jLoader;
+import com.aayushatharva.brotli4j.encoder.BrotliOutputStream;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.channels.ReadableByteChannel;
+import java.nio.charset.StandardCharsets;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class BrotliDecoderChannelTest {
+    private static final byte[] compressedData = new byte[]{-117, 1, -128, 77, 101, 111, 119, 3};
+
+    @BeforeAll
+    static void load() {
+        Brotli4jLoader.ensureAvailability();
+    }
+
+    @Test
+    public void decompress() throws IOException {
+        BrotliDecoderChannel channel = new BrotliDecoderChannel(new EntireBufferByteChannel(ByteBuffer.wrap(compressedData)));
+        ByteBuffer output = ByteBuffer.allocate(2048);
+        channel.read(output);
+        output.flip();
+        String result = StandardCharsets.UTF_8.decode(output).toString();
+        assertEquals("Meow", result);
+    }
+
+    @Test
+    public void decompressLonger() throws IOException {
+        String data = "In ancient times cats were worshipped as gods; they have not forgotten this.";
+        ByteBuffer compressed;
+
+        try (ByteArrayOutputStream baos = new ByteArrayOutputStream();
+             BrotliOutputStream output = new BrotliOutputStream(baos)) {
+            output.write(data.getBytes(StandardCharsets.UTF_8));
+            output.close();
+            compressed = ByteBuffer.wrap(baos.toByteArray());
+        }
+
+        // Quick verification that it compressed as expected
+        assertEquals(59, compressed.remaining());
+
+        BrotliDecoderChannel channel = new BrotliDecoderChannel(new EntireBufferByteChannel(compressed));
+        ByteBuffer output = ByteBuffer.allocate(2048);
+        channel.read(output);
+        output.flip();
+        String result = StandardCharsets.UTF_8.decode(output).toString();
+        assertEquals(data, result);
+    }
+
+    @Test
+    public void decompressOneByteAtATime() throws IOException {
+        BrotliDecoderChannel channel = new BrotliDecoderChannel(new OneByteAtATimeByteChannel(ByteBuffer.wrap(compressedData)));
+        ByteBuffer output = ByteBuffer.allocate(2048);
+        channel.read(output);
+        output.flip();
+        String result = StandardCharsets.UTF_8.decode(output).toString();
+        assertEquals("Meow", result);
+    }
+
+    @Test
+    public void decompressOneByteAtATimeLonger() throws IOException {
+        String data = "In ancient times cats were worshipped as gods; they have not forgotten this.";
+        ByteBuffer compressed;
+
+        try (ByteArrayOutputStream baos = new ByteArrayOutputStream();
+             BrotliOutputStream output = new BrotliOutputStream(baos)) {
+            output.write(data.getBytes(StandardCharsets.UTF_8));
+            output.close();
+            compressed = ByteBuffer.wrap(baos.toByteArray());
+        }
+
+        // Quick verification that it compressed as expected
+        assertEquals(59, compressed.remaining());
+
+        BrotliDecoderChannel channel = new BrotliDecoderChannel(new OneByteAtATimeByteChannel(compressed));
+        ByteBuffer output = ByteBuffer.allocate(2048);
+        channel.read(output);
+        output.flip();
+        String result = StandardCharsets.UTF_8.decode(output).toString();
+        assertEquals(data, result);
+    }
+
+    private static class EntireBufferByteChannel implements ReadableByteChannel {
+        private final ByteBuffer buffer;
+
+        public EntireBufferByteChannel(ByteBuffer buffer) {
+            this.buffer = buffer.slice();
+        }
+
+        @Override
+        public int read(ByteBuffer dst) {
+            if (!buffer.hasRemaining())
+                return -1;
+            int pos = dst.position();
+            dst.put(buffer);
+            return dst.position() - pos;
+        }
+
+        @Override
+        public boolean isOpen() {
+            return true;
+        }
+
+        @Override
+        public void close() {
+        }
+    }
+
+    private static class OneByteAtATimeByteChannel implements ReadableByteChannel {
+        private final ByteBuffer buffer;
+
+        public OneByteAtATimeByteChannel(ByteBuffer buffer) {
+            this.buffer = buffer.slice();
+        }
+
+        @Override
+        public boolean isOpen() {
+            return true;
+        }
+
+        @Override
+        public void close() {
+        }
+
+        @Override
+        public int read(ByteBuffer dst) {
+            if (!buffer.hasRemaining())
+                return -1;
+            dst.put(buffer.get());
+            return 1;
+        }
+    }
+}