Tests: print actual v. expected on test failure

The compress -3 test is failing on Windows.
This change will print a hex dump in a left/right format to help
triage the failed test.

tests/runtest.py

@@ -19,6 +19,67 @@ def main() -> None:
     else:
         test_decompress(args)
 
+def get_slice(data, line_no, size):
+    if len(data) / size > line_no:
+        return data[line_no:line_no + size]
+    elif len(data) / size == line_no:
+        return data[line_no:line_no + len(data) % size]
+    else:
+        return []
+
+def print_binary(data, size):
+    '''
+    Print hex
+    '''
+    lines = int(len(data) / size)
+
+    def render_slice(to_print, size):
+        line = ''
+        for byte in range(0, size):
+            if byte == size / 2:
+                line += ' '
+            if byte < len(to_print):
+                line += '{:02x}'.format(to_print[byte])
+            else:
+                line += '   '
+        return line
+
+    for line in range(0, lines):
+        print(render_slice(get_slice(data, line, size), size))
+    print('')
+
+def print_binary_compare(actual, expected, size):
+    '''
+    Print hex comparison of two buffers
+    '''
+    a_lines = int(len(actual) / size)
+    e_lines = int(len(expected) / size)
+    lines = max(a_lines, e_lines)
+
+    def render_slice(to_print, to_compare):
+        line = ''
+        for byte in range(0, size):
+            if byte == size / 2:
+                line += ' '
+            if byte < len(to_print):
+                if byte >= len(to_compare) or to_print[byte] != to_compare[byte]:
+                    line += '\x1b[1;33m{:02x}\x1b[0m'.format(to_print[byte])  # bold yellow
+                else:
+                    line += '{:02x}'.format(to_print[byte])                   # plain
+            else:
+                line += '  '
+        return line
+
+    for line in range(0, lines):
+        a_line = get_slice(actual, line, size)
+        e_line = get_slice(expected, line, size)
+        text_line = '{}  {}'.format(
+            render_slice(a_line, e_line),
+            render_slice(e_line, a_line)
+        )
+        print(text_line)
+    print('')
+
 
 def test_compress(args: argparse.Namespace) -> None:
     with open(args.reference, 'rb') as f:
@@ -27,17 +88,26 @@ def test_compress(args: argparse.Namespace) -> None:
     with open(args.input, 'rb') as f:
         input_ = f.read()
 
+    command = '{bzip2} {arg}'.format(
+        bzip2=args.bzip2,
+        arg=args.bzip_arg
+    )
+
+    print('\nRunning:  {}\n  with {} bytes of input from {}\n'.format(command, len(input_), args.input))
+
     p = subprocess.run(
-        [args.bzip2, args.bzip_arg],
+        command.split(' '),
         stdout=subprocess.PIPE,
         input=input_)
     if p.returncode != 0:
-        print('bzip2 failed to run', file=sys.stderr)
+        print('bzip2 failed to run')
         sys.exit(1)
 
     actual = p.stdout
     if actual != expected:
-        print('comparison of actual and expected output failed', file=sys.stderr)
+        print('comparison of actual and expected output failed')
+        print(' actual:' + ' ' * 60 + 'expected:')
+        print_binary_compare(actual, expected, 32)
         sys.exit(1)
 
 
@@ -50,24 +120,34 @@ def test_decompress(args: argparse.Namespace) -> None:
         stdout=subprocess.PIPE,
         input=input_)
     if p.returncode != 0:
-        print('bzip2 failed to compress', file=sys.stderr)
+        print('bzip2 failed to compress')
         sys.exit(1)
     compressed = p.stdout
     dargs = '-d' if args.bzip_arg != '-3' else '-ds'
+
+    command = '{bzip2} {arg}'.format(
+        bzip2=args.bzip2,
+        arg=dargs
+    )
+
+    print('\nRunning:  {}\n  with {} bytes of input from {}\n'.format(command, len(input_), args.input))
+
     p = subprocess.run(
-        [args.bzip2, dargs],
+        command.split(' '),
         stdout=subprocess.PIPE,
         input=compressed,
     )
     if p.returncode != 0:
-        print('bzip2 failed to decompress', file=sys.stderr)
+        print('bzip2 failed to decompress')
         sys.exit(1)
 
     actual = p.stdout
     if input_ != actual:
-        print('comparison of actual and expected output failed', file=sys.stderr)
+        print('comparison of actual and expected output failed')
+        print(' actual:' + ' ' * 60 + 'input:')
+        print_binary_compare(actual, input_, 32)
         sys.exit(1)
 
 
 if __name__ == "__main__":
-    main()
+    main()