incorrect behaviour of expect_output()?

[famuvie]

tf <- function() cat('my output')  # test function
expect_output(tf(), 'output')       # passes, as expected
expect_output(tf(), 'xxx')            # error, as expected
# Error: tf() does not match 'xxx'. Actual value: "my output"
expect_output(tf(), NA)              # passes. Expected error. 
expect_output(tf())                     # fails. Expected pass. 
# Error in identical(regexp, NA) : 
#   argument "regexp" missing, without default value
packageVersion('testthat')
# [1] ‘0.11.0.9000’

In the last two expectations:

• NA means expect no output, however, it passes.
• omitted regexp means expect some output, however it fails.

[richierocks]

I can reproduce that the documentation doesn't match the behaviour when regexp is missing.

You can use regexp = "" to match anything as a workaround.

[hadley]

Hmmm, the problem with expect_output(tf(), NA) is that expect_output() always prints the input, so as far as I can tell there's no case in which code won't create output.

[hadley]

Hmmm, the problem with expect_output(tf(), NA) is that expect_output() always prints the input, so as far as I can tell there's no case in which code won't create output.

I'm thinking the next version of testthat will be 1.0.0 so it's probably ok to change this behaviour to force the user to print() the object if they want to inspect the output.