How to test Python readline completion?
I'm writing a command-line interface in Python. It uses the readline module to provide command history and completion.
While everything works fine in interactive mode, I'd like to run automated tests on the completion feature. My naive first try involved using a file for standard input:
my_app < command.file
The command file contained a tab, in the hopes that it would invoke the completion feature. No luck. What's the right way to do the testing?
For this I would use Pexpect (Python version of Expect). The readline library needs to be speaking to a terminal to do interactive tab-completion and such—it can't do this if it is only getting one-way input from a redirected file.
Pexpect works for this because it creates a pseudo terminal, which consists of two parts: the slave, where the program you are testing runs, and the master, where the Python pexpect code runs. The pexpect code emulates the human running the test program. It is responsible for sending characters to the slave, including characters such as newline and tab, and reacting to the expected output (this is where the phrase "expect" comes from).
See the program ftp.py from the examples directory for a good example of how you would control your test program from within expect. Here is a sample of the code:
child = pexpect.spawn('ftp ftp.openbsd.org')
child.expect('(?i)name .*: ')
child.sendline('anonymous')
child.expect('(?i)password')
child.sendline('pexpect@sourceforge.net')
child.expect('ftp> ')
rlcompleter might accomplish what you want
From the documentation:
The rlcompleter module is designed for use with Python's interactive mode. A user can add the following lines to his or her initialization file (identified by the PYTHONSTARTUP environment variable) to get automatic Tab completion:
try:
import readline
except ImportError:
print "Module readline not available."
else:
import rlcompleter
readline.parse_and_bind("tab: complete")
https://docs.python.org/2/library/rlcompleter.html
Check out ScriptTest:
from scripttest import TestFileEnvironment
env = TestFileEnvironment('./scratch')
def test_script():
env.reset()
result = env.run('do_awesome_thing testfile --with extra_win --file %s' % filename)
And play around with passing the arguments as you please.
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