Added a simple test suite for gzip. It simply opens a temp file,

writes a chunk of compressed data, closes it, writes another chunk, and
reads the contents back to verify that they are the same.

Lib/test/test_gzip.py

@@ -0,0 +1,30 @@
+
+import sys, os
+import gzip, tempfile
+
+filename = tempfile.mktemp()
+
+data1 = """  int length=DEFAULTALLOC, err = Z_OK;
+  PyObject *RetVal;
+  int flushmode = Z_FINISH;
+  unsigned long start_total_out;
+
+"""
+
+data2 = """/* zlibmodule.c -- gzip-compatible data compression */
+/* See http://www.cdrom.com/pub/infozip/zlib/ */
+/* See http://www.winimage.com/zLibDll for Windows */
+"""
+
+f = gzip.GzipFile(filename, 'w') ; f.write(data1) ; f.close()
+
+f = gzip.GzipFile(filename, 'r') ; d = f.read() ; f.close()
+assert d == data1
+
+# Append to the previous file
+f = gzip.GzipFile(filename, 'a') ; f.write(data2) ; f.close()
+
+f = gzip.GzipFile(filename, 'r') ; d = f.read() ; f.close()
+assert d == data1+data2
+
+os.unlink( filename )