Fix java/util/zip/DeflateIn_InflateOut.skipBytes Test

java/util/zip/DeflateIn_InflateOut.skipBytes verifies functionality of
DeflaterInputStream.skipBytes. While testing skipping of bytes, test
uses different input data with same data length, and compares the
compressed sizes of these data to verify skipping bytes. As per zlib
specification which is what is used by Deflater in java, length of
compressed data is highly dependable on input data contents, so it will
be incorrect to assume that compression ratio would be constant for same
length input data. For more details please see explaination in
eclipse-openj9/openj9#14948 (comment).

Signed-off-by: Rahil Shah <rahil@ca.ibm.com>

test/jdk/java/util/zip/DeflateIn_InflateOut.java

@@ -41,21 +41,24 @@ public class DeflateIn_InflateOut {
     private static ByteArrayOutputStream baos;
     private static InflaterOutputStream ios;
 
-    private static void reset() {
-        new Random(new Date().getTime()).nextBytes(data);
-
+    private static void resetStreams() {
         bais = new ByteArrayInputStream(data);
         dis = new DeflaterInputStream(bais);
 
         baos = new ByteArrayOutputStream();
         ios = new InflaterOutputStream(baos);
     }
 
+    private static void resetAll() {
+        new Random(new Date().getTime()).nextBytes(data);
+        resetStreams();
+    }
+
     /** Check byte arrays read/write. */
     private static void ArrayReadWrite() throws Throwable {
         byte[] buf = new byte[512];
 
-        reset();
+        resetAll();
         check(dis.available() == 1);
         for (;;) {
             int len = dis.read(buf, 0, buf.length);
@@ -74,7 +77,7 @@ private static void ArrayReadWrite() throws Throwable {
     private static void ArrayReadByteWrite() throws Throwable {
         byte[] buf = new byte[512];
 
-        reset();
+        resetAll();
         for (;;) {
             int len = dis.read(buf, 0, buf.length);
             if (len <= 0) {
@@ -100,7 +103,7 @@ private static void ByteReadArrayWrite() throws Throwable {
         byte[] buf = new byte[8192];
         int off = 0;
 
-        reset();
+        resetAll();
         int datum = dis.read();
         while (datum != -1) {
             if (off == 8192) {
@@ -126,7 +129,7 @@ private static void ByteReadByteWrite() throws Throwable {
         byte[] buf = new byte[512];
         boolean reachEOF = false;
 
-        reset();
+        resetAll();
         while (dis.available() == 1) {
             int datum = dis.read();
             if (datum == -1) {
@@ -149,7 +152,9 @@ private static void SkipBytes() throws Throwable {
         int numReadable = 0;
 
         // Count number of bytes that are read
-        reset();
+
+		// Reset Input data and Streams
+        resetAll();
         check(dis.available() == 1);
         for (;;) {
             int count = dis.read(buf, 0, buf.length);
@@ -162,7 +167,13 @@ private static void SkipBytes() throws Throwable {
         check(dis.available() == 0);
 
         // Verify that skipping the first several bytes works.
-        reset();
+
+        // Different input data even though is of fixed size would lead to
+        // different compressed output. The main intention of this method to
+        // test DeflaterInputStream.skipBytes so keeping the input data fixed
+        // while testing out skipping of different bytes and only need to reset
+        // the input streams.
+        resetStreams();
         int numNotSkipped = 0;
         int numSkipBytes = 2053; // arbitrarily chosen prime
         check(dis.skip(numSkipBytes) == numSkipBytes);
@@ -177,7 +188,7 @@ private static void SkipBytes() throws Throwable {
         check(numNotSkipped + numSkipBytes == numReadable);
 
         // Verify that skipping some bytes mid-stream works.
-        reset();
+        resetStreams();
         numNotSkipped = 0;
         numSkipBytes = 8887; // arbitrarily chosen prime
         for (int i = 0; ; i++) {
@@ -195,7 +206,7 @@ private static void SkipBytes() throws Throwable {
         check(numNotSkipped + numSkipBytes == numReadable);
 
         // Verify that skipping the last N bytes works.
-        reset();
+        resetStreams();
         numNotSkipped = 0;
         numSkipBytes = 6449; // arbitrarily chosen prime
         for (int i = 0; ; i++) {