Add IO class.

With io.write(), can start writing tests now.

runtests

@@ -0,0 +1,187 @@
+#!/usr/bin/python
+
+from collections import defaultdict
+from os import listdir
+from os.path import abspath, dirname, isdir, isfile, join, realpath, relpath, splitext
+import re
+from subprocess import Popen, PIPE
+import sys
+
+# Runs the tests.
+WREN_DIR = dirname(realpath(__file__))
+TEST_DIR = join(WREN_DIR, 'test')
+
+if sys.platform == 'win32':
+  WREN_APP = join(WREN_DIR, 'Debug', 'wren.exe')
+  if not isfile(WREN_DIR):
+    WREN_APP = join(WREN_DIR, 'Release', 'wren.exe')
+  if not isfile(WREN_APP):
+    sys.exit('Cannot find wren.exe!')
+elif sys.platform.startswith('linux'):
+  WREN_APP = join(WREN_DIR, '1', 'out', 'Debug', 'wren')
+  if not isfile(WREN_APP):
+    WREN_APP = join(WREN_DIR, '1', 'out', 'Release', 'wren')
+  if not isfile(WREN_APP):
+    sys.exit('Cannot find wren!')
+elif sys.platform.startswith('darwin'):
+  WREN_APP = join(WREN_DIR, 'build', 'Debug', 'wren')
+  if not isfile(WREN_APP):
+    WREN_APP = join(WREN_DIR, 'build', 'Release', 'wren')
+  if not isfile(WREN_APP):
+    sys.exit('Cannot find wren!')
+else:
+  sys.exit('System not supported!')
+
+EXPECT_PATTERN = re.compile(r'// expect: (.*)')
+SKIP_PATTERN = re.compile(r'// skip: (.*)')
+NONTEST_PATTERN = re.compile(r'// nontest')
+
+if sys.platform == 'win32':
+  class color:
+    GREEN = ''
+    RED = ''
+    DEFAULT = ''
+    PINK = ''
+    YELLOW = ''
+else:
+  class color:
+    GREEN = '\033[32m'
+    RED = '\033[31m'
+    DEFAULT = '\033[0m'
+    PINK = '\033[91m'
+    YELLOW = '\033[33m'
+
+passed = 0
+failed = 0
+skipped = defaultdict(int)
+num_skipped = 0;
+
+
+def walk(dir, callback):
+  """ Walks [dir], and executes [callback] on each file. """
+  dir = abspath(dir)
+  for file in [file for file in listdir(dir) if not file in [".",".."]]:
+    nfile = join(dir, file)
+    if isdir(nfile):
+      walk(nfile, callback)
+    else:
+      callback(nfile)
+
+
+def print_line(line=None):
+  # Erase the line.
+  print '\033[2K',
+  # Move the cursor to the beginning.
+  print '\r',
+  if line:
+    print line,
+    sys.stdout.flush()
+
+
+def run_test(path):
+  global passed
+  global failed
+  global skipped
+  global num_skipped
+
+  if (splitext(path)[1] != '.wren'):
+    return
+
+  # Check if we are just running a subset of the tests.
+  if len(sys.argv) == 2:
+    this_test = relpath(path, join(WREN_DIR, 'test'))
+    if not this_test.startswith(sys.argv[1]):
+      return
+
+  # Make a nice short path relative to the working directory.
+  path = relpath(path)
+
+  # Read the test and parse out the expectations.
+  expect_output = []
+  expect_error = []
+  expect_return = 0
+
+  print_line('Passed: ' + color.GREEN + str(passed) + color.DEFAULT +
+         ' Failed: ' + color.RED + str(failed) + color.DEFAULT +
+         ' Skipped: ' + color.YELLOW + str(num_skipped) + color.DEFAULT)
+
+  line_num = 1
+  with open(path, 'r') as file:
+    for line in file:
+      match = EXPECT_PATTERN.search(line)
+      if match:
+          expect_output.append((match.group(1), line_num))
+
+      match = SKIP_PATTERN.search(line)
+      if match:
+        num_skipped += 1
+        skipped[match.group(1)] += 1
+        return
+
+      match = NONTEST_PATTERN.search(line)
+      if match:
+        # Not a test file at all, so ignore it.
+        return
+
+      line_num += 1
+
+  # Invoke wren and run the test.
+  proc = Popen([WREN_APP, path], stdout=PIPE, stderr=PIPE)
+  (out, err) = proc.communicate()
+  (out, err) = out.replace('\r\n', '\n'),  err.replace('\r\n', '\n')
+
+  fails = []
+
+  # Validate the exit code.
+  if proc.returncode != 0:
+    fails.append('Expected return code 0 and got {0}.'.
+      format(proc.returncode))
+  else:
+    # Validate the output.
+    expect_index = 0
+
+    # Remove the trailing last empty line.
+    out_lines = out.split('\n')
+    if out_lines[-1] == '':
+        del out_lines[-1]
+
+    for line in out_lines:
+        if expect_index >= len(expect_output):
+            fails.append('Got output "{0}" when none was expected.'.
+                format(line))
+        elif expect_output[expect_index][0] != line:
+            fails.append('Expected output "{0}" on line {1} and got "{2}".'.
+                format(expect_output[expect_index][0],
+                       expect_output[expect_index][1], line))
+        expect_index += 1
+
+    while expect_index < len(expect_output):
+        fails.append('Missing expected output "{0}" on line {1}.'.
+            format(expect_output[expect_index][0],
+                   expect_output[expect_index][1]))
+        expect_index += 1
+
+  # Display the results.
+  if len(fails) == 0:
+    passed += 1
+    print color.GREEN + 'PASS' + color.DEFAULT + ': ' + path
+  else:
+    failed += 1
+    print_line(color.RED + 'FAIL' + color.DEFAULT + ': ' + path)
+    print
+    for fail in fails:
+      print '     ', color.PINK + fail + color.DEFAULT
+    print
+
+walk(TEST_DIR, run_test)
+
+print_line()
+if failed == 0:
+  print 'All ' + color.GREEN + str(passed) + color.DEFAULT + ' tests passed.'
+else:
+  print (color.GREEN + str(passed) + color.DEFAULT + ' tests passed. ' +
+       color.RED + str(failed) + color.DEFAULT + ' tests failed.')
+
+for key in sorted(skipped.keys()):
+  print ('Skipped ' + color.YELLOW + str(skipped[key]) + color.DEFAULT +
+       ' tests: ' + key)