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Testing GIF Byte Manipulation Utilities in Glide Decoder

This test suite validates the GifBytesTestUtil class in Glide’s GIF decoder implementation, ensuring accurate byte-level manipulation for GIF image processing. The tests verify header writing, image descriptor formatting, and color table handling.

Test Coverage Overview

The test suite provides comprehensive coverage of GIF byte manipulation functionality:

Header and Logical Screen Descriptor (LSD) writing with and without Global Color Table
Image descriptor generation with various parameters
Color table writing and validation
Graphics Control Extension block formatting
Fake image data generation for testing

Implementation Analysis

The testing approach uses JUnit4 framework with byte-level precision testing. Each test method focuses on specific GIF structure components, using ByteBuffer for memory manipulation and explicit byte array comparisons. The implementation leverages direct byte value assertions to ensure exact binary output.

Technical Details

Testing tools and configuration:

JUnit4 test runner and assertions
ByteBuffer for memory allocation and manipulation
Custom assertEquals method for byte array comparison
Hexadecimal byte value verification
Static utility methods for GIF structure generation

Best Practices Demonstrated

The test suite exemplifies several testing best practices:

Isolated test cases for each GIF component
Explicit expected vs actual value comparisons
Comprehensive edge case handling
Clear test method naming conventions
Detailed error messages in assertions

bumptech/glide

third_party/gif_decoder/src/test/java/com/bumptech/glide/gifdecoder/test/GifBytesTestUtilTest.java

            
package com.bumptech.glide.gifdecoder.test;

import static org.junit.Assert.assertArrayEquals;

import java.nio.ByteBuffer;
import java.util.Arrays;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.JUnit4;

/**
 * Tests for {@link com.bumptech.glide.gifdecoder.test.GifBytesTestUtil}.
 */
@RunWith(JUnit4.class)
public class GifBytesTestUtilTest {

  @Test
  public void testWriteHeaderAndLsdWithoutGct() {
    ByteBuffer buffer = ByteBuffer.allocate(GifBytesTestUtil.HEADER_LENGTH);
    GifBytesTestUtil.writeHeaderAndLsd(buffer, 8, 16, false, 0);

    byte[] expected =
        new byte[] { 0x47, 0x49, 0x46, 0x38, 0x39, 0x61, 0x00, 0x08, 0x00, 0x10, 0x20, 0x00, 0x00 };

    assertEquals(expected, buffer);
  }

  @Test
  public void testWriteHeaderAndLsdWithGct() {
    ByteBuffer buffer = ByteBuffer.allocate(GifBytesTestUtil.HEADER_LENGTH);
    GifBytesTestUtil.writeHeaderAndLsd(buffer, 8, 16, true, 4);

    byte[] expected =
        new byte[] { 0x47, 0x49, 0x46, 0x38, 0x39, 0x61, 0x00, 0x08, 0x00, 0x10, (byte) 0xA4, 0x00,
            0x00 };

    assertEquals(expected, buffer);
  }

  @Test
  public void testWriteImageDescriptorWithoutColorTable() {
    ByteBuffer buffer = ByteBuffer.allocate(GifBytesTestUtil.IMAGE_DESCRIPTOR_LENGTH);
    GifBytesTestUtil.writeImageDescriptor(buffer, 10, 9, 8, 7, false, 0);

    byte[] expected = new byte[] {
        // Image separator.
        0x2C,
        // Image left.
        0x00, 0x0A,
        // Image right.
        0x00, 0X09,
        // Image width.
        0x00, 0x08,
        // Image height.
        0x00, 0x07,
        // Packed field.
        0x00 };

    assertEquals(expected, buffer);
  }

  @Test
  public void testWriteImageDescriptorWithColorTable() {
    ByteBuffer buffer = ByteBuffer.allocate(GifBytesTestUtil.IMAGE_DESCRIPTOR_LENGTH);
    GifBytesTestUtil.writeImageDescriptor(buffer, 10, 9, 8, 7, true, 4);

    byte packedField =
        // Set LCT flag
        (byte) 0x80
            // Size of color table (2^(N + 1) == 4)
            | 0x01;

    byte[] expected = new byte[] {
        // Image separator.
        0x2C,
        // Image left.
        0x00, 0x0A,
        // Image right.
        0x00, 0X09,
        // Image width.
        0x00, 0x08,
        // Image height.
        0x00, 0x07, packedField };

    assertEquals(expected, buffer);
  }

  @Test
  public void testWriteColorTable() {
    final int numColors = 4;
    ByteBuffer buffer = ByteBuffer.allocate(GifBytesTestUtil.getColorTableLength(numColors));
    GifBytesTestUtil.writeColorTable(buffer, numColors);

    byte[] expected = new byte[] {
        // First color.
        0x00, 0x00, 0x00,
        // Second color.
        0x00, 0x00, 0x01,
        // Third color.
        0x00, 0x00, 0x02,
        // Fourth color.
        0x00, 0x00, 0x03, };


    assertEquals(expected, buffer);
  }

  @Test
  public void testWriteFakeImageData() {
    ByteBuffer buffer = ByteBuffer.allocate(4);
    GifBytesTestUtil.writeFakeImageData(buffer, 2);

    byte[] expected = new byte[] { 0x02, 0x01, 0x01, 0x00 };

    assertEquals(expected, buffer);
  }

  @Test
  public void testWritesGraphicsControlExtension() {
    short delay = 20;
    ByteBuffer buffer = ByteBuffer.allocate(GifBytesTestUtil.GRAPHICS_CONTROL_EXTENSION_LENGTH);
    byte[] expected = new byte[] {
        // Extension inducer.
        0x21,
        // Graphic control label.
        (byte) 0xF9,
        // Block size.
        0x04,
        // Packed byte.
        0x00,
        // Frame delay.
        0x00, 0x14,
        // Transparent color index.
        0x00,
        // block terminator.
        0x00 };

    GifBytesTestUtil.writeGraphicsControlExtension(buffer, delay);
    assertEquals(expected, buffer);
  }

  private static void assertEquals(byte[] expected, ByteBuffer buffer) {
    assertArrayEquals(
        "expected=" + Arrays.toString(expected) + " received=" + Arrays.toString(buffer.array()),
        expected, buffer.array());
  }
}