testthat (version 2.0.0)

expect_known_output: Expectations: is the output or the value equal to a known good value?

Description

For complex printed output and objects, it is often challenging to describe exactly what you expect to see. expect_known_value() and expect_known_output() provide a slightly weaker guarantee, simply asserting that the values have no changed since the last time that you ran them.

Usage

expect_known_output(object, file, update = TRUE, ..., info = NULL,
  label = NULL, print = FALSE, width = 80)
expect_known_value(object, file, update = TRUE, ..., info = NULL,
  label = NULL)
expect_known_hash(object, hash = NULL)

Arguments

object

object to test

file

File path where known value/output will be stored.

update

Should the file be updated? Defaults to TRUE, with the expectation that you'll notice changes because of the first failure, and then see the modified files in git.

...

other values passed to all.equal()

info

extra information to be included in the message (useful when writing tests in loops).

label

object label. When NULL, computed from deparsed object.

print

If TRUE and the result of evaluating code is visible this will print the result, ensuring that the output of printing the object is included in the overall output

width

Number of characters per line of output

hash

Known hash value. Leave empty and you'll be informed what to use in the test output.

Details

These expectations should be used in conjunction with git, as otherwise there is no way to revert to previous values. Git is particularly useful in conjunction with expect_known_output() as the diffs will show you exactly what has changed.

Note that known values updates will only updated when running tests interactively. R CMD check clones the package source so any changes to the reference files will occured a temporary directory, and will not be synchronised back to the source package.

Examples

# NOT RUN {
tmp <- tempfile()

# The first run always succeeds
expect_known_output(mtcars[1:10, ], tmp, print = TRUE)

# Subsequent runs will suceed only if the file is unchanged
# This will succeed:
expect_known_output(mtcars[1:10, ], tmp, print = TRUE)

# }
# NOT RUN {
# This will fail
expect_known_output(mtcars[1:9, ], tmp, print = TRUE)
# }