DataHandleTest: expose internal API to subclasses

The SciJava coding style strongly encourages private over protected
methods and fields:
https://imagej.net/Coding_style#Private_over_protected_fields_and_methods

However, for test scope things, the impact is less, and the promise of
API compatibility in the future according to SemVer does not exist.
So we are less concerned about breakages.

Signed-off-by: Curtis Rueden <ctrueden@wisc.edu>

Author: gab1one

src/test/java/org/scijava/io/handle/DataHandleTest.java

@@ -53,7 +53,7 @@
  */
 public abstract class DataHandleTest {
 
-	private static final byte[] BYTES = { //
+	protected static final byte[] BYTES = { //
 		'H', 'e', 'l', 'l', 'o', ',', ' ', 'w', 'o', 'r', 'l', 'd', '\n', //
 			9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 0, -128, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, //
 			125, 127, -127, -125, -3, -2, -1 };
@@ -208,9 +208,9 @@ protected <L extends Location> void checkWrites(final DataHandle<L> handle)
 		}
 	}
 
-	// -- Helper methods --
+	// -- Internal methods --
 
-	private void assertBytesMatch(final int offset, final int length,
+	protected void assertBytesMatch(final int offset, final int length,
 		final byte[] b)
 	{
 		assertEquals(length, b.length);
@@ -219,7 +219,7 @@ private void assertBytesMatch(final int offset, final int length,
 		}
 	}
 
-	private String msg(final int i) {
+	protected String msg(final int i) {
 		return "[" + i + "]:";
 	}