DfsPackFileMidx tests: Compare byte[] for checksum

We cannot precalculate the checkum of the midx, because it includes
the file names and these change between tests. The test validates that
the first 4 bytes are not the header (MIDX), so at least we are not
reading from the beginning of the buffer. It compares 4 bytes
independently and we run the risk of finding them by chance in the
actual checksum.

Compare the 4 bytes as array, so we fail only if the 4 of them match.

Change-Id: Id26a7722bb564670db68dc3102b38f8b6a6a6964

Author: ifradeo

org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/DfsPackFileMidxNPacksTest.java

@@ -20,7 +20,6 @@
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
-import static org.junit.Assert.assertNotEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertThrows;
@@ -1054,10 +1053,9 @@ public void getChecksum() throws Exception {
 			byte[] checksum = midx.getChecksum(ctx);
 			assertNotNull(checksum);
 			assertEquals(20, checksum.length);
-			assertNotEquals('M', checksum[0]);
-			assertNotEquals('I', checksum[1]);
-			assertNotEquals('D', checksum[2]);
-			assertNotEquals('X', checksum[3]);
+
+			byte[] mdixHeader = { 'M', 'I', 'D', 'X' };
+			assertFalse(Arrays.equals(mdixHeader, 0, 4, checksum, 0, 4));
 		}
 	}
 

org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/DfsPackFileMidxSingleTest.java

@@ -20,7 +20,6 @@
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
-import static org.junit.Assert.assertNotEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertThrows;
@@ -1023,10 +1022,9 @@ public void getChecksum() throws Exception {
 			byte[] checksum = midx.getChecksum(ctx);
 			assertNotNull(checksum);
 			assertEquals(20, checksum.length);
-			assertNotEquals('M', checksum[0]);
-			assertNotEquals('I', checksum[1]);
-			assertNotEquals('D', checksum[2]);
-			assertNotEquals('X', checksum[3]);
+
+			byte[] mdixHeader = { 'M', 'I', 'D', 'X' };
+			assertFalse(Arrays.equals(mdixHeader, 0, 4, checksum, 0, 4));
 		}
 	}