Assert that certain conditions are true.

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Description

assert_that is a drop-in replacement for stopifnot but is designed to give informative error messages.

Usage

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Arguments

...

unnamed expressions that describe the conditions to be tested. Rather than combining expressions with &&, separate them by commas so that better error messages can be generated.

env

(advanced use only) the environment in which to evaluate the assertions.

Assertions

Assertion functions should return a single TRUE or FALSE: any other result is an error, and assert_that will complain about it. This will always be the case for the assertions provided by assertthat, but you may need be a more careful for base R functions.

To make your own assertions that work with assert_that, see the help for on_failure.

See Also

validate_that, which returns a message (not an error) if the condition is false.

Examples

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x <- 1
# assert_that() generates errors, so can't be usefully run in
# examples
## Not run: 
assert_that(is.character(x))
assert_that(length(x) == 3)
assert_that(is.dir("asdf"))
y <- tempfile()
writeLines("", y)
assert_that(is.dir(y))

## End(Not run)

# But see_if just returns the values, so you'll see that a lot
# in the examples: but remember to use assert_that in your code.
see_if(is.character(x))
see_if(length(x) == 3)
see_if(is.dir(17))
see_if(is.dir("asdf"))