How can I see print() statements in behave (BDD)
Context: I am using Python with Behave (BDD).
Whether I run my tests from the command line (behave) or from a custom main(), the behavior is the same: the test runs and the only output that I see in the console is the standard BDD report.
My tests include print() statements that help me debug my code. However, none of these print statements are being displayed in the console output when I run behave.
Is there any way we can have "behave" display the print statements in our code?
My Main()
config = Configuration()
if not config.format:
default_format = config.defaults["default_format"]
config.format = [ default_format ]
config.verbose = True
r = runner.Runner(config)
r.run()
if config.show_snippets and r.undefined_steps:
print_undefined_step_snippets(r.undefined_steps)
My test.feature file:
Feature: My test feature with the Behave BDD
Scenario: A simple test
Given you are happy
When someone says hi
Then you smile
My test_steps.py file:
from behave import given, when, then, step, model
@given('you are happy')
def step_impl(context):
pass
@when ('someone says {s}')
def step_impl(context, s):
context.message = s
print("THIS IS NEVER DISPLAYED IN THE CONSOLE")
pass
@then ('you smile')
def step_impl(context):
assert(context.message == "hi")
Solution 1:
from command line, you can use the following:
--no-capture
for any stdout output to be printed immediately.
--no-capture-stderr
for any stderr output to be printed immediately.
Solution 2:
The first thing to do is to prevent capture of stdout
(and maybe also stderr
) as explained by Xuan or Ben.
However, there's a further complication that will stump people who are not aware of it. By default, behave
outputs its report in color. This is problematic because the way it works is that when it runs a step, it first prints out the line of the step in a neutral color that indicates it does not yet know whether the step has passed or not. Once the step has finished, it uses escape codes to overwrite the previous line with a new color. If you don't do something to work around it, behave
may simply overwrite what your print
statement produced, and it may be difficult to figure out what happened.
In the following illustrations, I'm going to put the color in brackets at the end of the line. If you do not use print
, the step "do something" would appear like this, before it is executed:
When do something [gray]
And once executed it would be replaced with a green line:
When do something [green]
behave
outputs an escape sequence that makes the terminal go up and overwrite the line with a new color. No problem there.
If you put print "foo"
in your step, the terminal would contain this, just before the step is completed:
When do something [gray]
foo
And then when the step completes successfully this is what you'd see on the terminal:
When do something [gray]
When do something [green]
The same escape sequence has caused behave
to overwrite the output produced by the print
statement.
I've used two methods to work around the issue in addition to turning off stdout
capture:
Use the
--no-color
option. This turns off the escape sequences and yourprint
statements should produce visible output.Add a few extra newlines at the end of a
print
. Soprint "foo\n\n"
, for instance.behave
will overwrite a useless blank line instead of overwriting the information you want. This is what I end up doing most often because I never invokebehave
directly and adding a single additional option tobehave
's invocation, or editing a settings file is more cumbersome than just adding a few newlines toprint
.
Solution 3:
I figured it out after spending more time reading the documentation. It is actually quite simple. By default, behave
does not display any output (i.e. by using print()
) unless there is a failure in the test.
To force displaying all output regardless of the outcome of the test (pass/fail), all you need is to change some of the default settings. The easiest way to achieve that is to create a file named behave.ini
in the root of your project's directory and put the following:
Filename: behave.ini
[behave]
stderr_capture=False
stdout_capture=False
Next time you run your behave tests, you will see all outputs from your debug statements whether your tests pass or fail.