Add implicit conversion from integral types to byte array

Integral types are converted to a byte array with a Big Endian byte
order and size as the number of bytes used to represent the integral
value in two's complement binary form.

Issue: junit-team#2702

junit-jupiter-params/src/main/java/org/junit/jupiter/params/converter/DefaultArgumentConverter.java

@@ -22,6 +22,8 @@
 import java.net.MalformedURLException;
 import java.net.URI;
 import java.net.URL;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
 import java.nio.charset.Charset;
 import java.nio.file.Path;
 import java.nio.file.Paths;
@@ -64,6 +66,12 @@
  * {@link File}, {@link BigDecimal}, {@link BigInteger}, {@link Currency},
  * {@link Locale}, {@link URI}, {@link URL}, {@link UUID}, etc.
  *
+ * <p>The {@code DefaultArgumentConverter} can also convert from primitive
+ * integral types (byte, short, int and long) and their corresponding wrapper
+ * types to a byte array, having {@link ByteOrder#BIG_ENDIAN BIG_ENDIAN} byte
+ * order and size equals to the number of bytes used to represent the integral
+ * value in two's complement binary form.
+ *
  * <p>If the source and target types are identical the source object will not
  * be modified.
  *
@@ -84,6 +92,8 @@ public class DefaultArgumentConverter extends SimpleArgumentConverter {
 		new FallbackStringToObjectConverter() //
 	));
 
+	private static final IntegralTypesToByteArrayConverter integralTypesToByteArrayConverter = new IntegralTypesToByteArrayConverter();
+
 	private DefaultArgumentConverter() {
 		// nothing to initialize
 	}
@@ -124,6 +134,9 @@ private Object convertToTargetType(Object source, Class<?> targetType) {
 				}
 			}
 		}
+		if (targetType == byte[].class && integralTypesToByteArrayConverter.canConvert(source.getClass())) {
+			return integralTypesToByteArrayConverter.convert(source);
+		}
 		throw new ArgumentConversionException("No implicit conversion to convert object of type "
 				+ source.getClass().getName() + " to type " + targetType.getName());
 	}
@@ -299,4 +312,29 @@ private static URL toURL(String url) {
 
 	}
 
+	private static class IntegralTypesToByteArrayConverter {
+
+		private boolean canConvert(Class<?> sourceType) {
+			return sourceType == Byte.class || sourceType == Short.class || sourceType == Integer.class
+					|| sourceType == Long.class;
+		}
+
+		private byte[] convert(Object source) {
+			if (source instanceof Byte) {
+				return ByteBuffer.allocate(Byte.BYTES).put((Byte) source).array();
+			}
+			if (source instanceof Short) {
+				return ByteBuffer.allocate(Short.BYTES).putShort((Short) source).array();
+			}
+			if (source instanceof Integer) {
+				return ByteBuffer.allocate(Integer.BYTES).putInt((Integer) source).array();
+			}
+			if (source instanceof Long) {
+				return ByteBuffer.allocate(Long.BYTES).putLong((Long) source).array();
+			}
+			throw new ArgumentConversionException("Cannot convert object of type " + source.getClass().getName());
+		}
+
+	}
+
 }

junit-jupiter-params/src/test/java/org/junit/jupiter/params/converter/DefaultArgumentConverterTests.java

@@ -231,6 +231,17 @@ void convertsStringToUUID() {
 
 	// -------------------------------------------------------------------------
 
+	/**
+	 * @since FIXME
+	 */
+	@Test
+	void convertsIntegralTypesToByteArray() {
+		assertConverts((byte) 0x7F, byte[].class, new byte[] { 127 });
+		assertConverts((short) 0x7E7F, byte[].class, new byte[] { 126, 127 });
+		assertConverts(0x7C7D7E7F, byte[].class, new byte[] { 124, 125, 126, 127 });
+		assertConverts(0x78797A7B7C7D7E7FL, byte[].class, new byte[] { 120, 121, 122, 123, 124, 125, 126, 127 });
+	}
+
 	private void assertConverts(Object input, Class<?> targetClass, Object expectedOutput) {
 		var result = DefaultArgumentConverter.INSTANCE.convert(input, targetClass);