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% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/testit.R
\name{assert}
\alias{assert}
\alias{\%==\%}
\title{Assertions with an optional message}
\usage{
assert(fact, ...)
x \%==\% y
}
\arguments{
\item{fact}{A message for the assertions when any of them fails; treated the
same way as expressions in \code{...} if it is not a character string,
which means you are not required to provide a message to this function.}
\item{...}{An R expression; see Details.}
\item{x, y}{two R objects to be compared}
}
\value{
For \code{assert()}, invisible \code{NULL} if all expressions
returned \code{TRUE}, otherwise an error is signaled and the user-provided
message is emitted. For \code{\%==\%}, \code{TRUE} or \code{FALSE}.
}
\description{
The function \code{assert()} was inspired by \code{\link{stopifnot}()}. It
emits a message in case of errors, which can be a helpful hint for diagnosing
the errors (\code{stopifnot()} only prints the possibly truncated source code
of the expressions).
The infix operator \code{\%==\%} is simply an alias of the
\code{\link{identical}()} function to make it slightly easier and intuitive
to write test conditions. \code{x \%==\% y} is the same as
\code{identical(x, y)}. When it is used inside \code{assert()}, a message
will be printed if the returned value is not \code{TRUE}, to show the
values of the LHS (\code{x}) and RHS (\code{y}) via \code{\link{str}()},
which can be helpful for you to check why the assertion failed.
}
\details{
For the \code{...} argument, it should be a single R expression wrapped in
\code{{}}. This expression may contain multiple sub-expressions. A
sub-expression is treated as a test condition if it is wrapped in \code{()}
(meaning its value will be checked to see if it is a logical vector
containing any \code{FALSE} values) , otherwise it is evaluated in the normal
way and its value will not be checked. If the value of the last
sub-expression is logical, it will also be treated as a test condition.
}
\note{
The internal implementation of \code{assert()} is different with the
\code{stopifnot()} function in R \pkg{base}: (1) the custom message
\code{fact} is emitted if an error occurs; (2) \code{assert()} requires the
logical values to be non-empty (\code{logical(0)} will trigger an error);
(3) if \code{...} contains a compound expression in \code{{}} that returns
\code{FALSE} (e.g., \code{if (TRUE) {1+1; FALSE}}), the first and the last
but one line of the source code from \code{\link{deparse}()} are printed in
the error message, otherwise the first line is printed; (4) the arguments
in \code{...} are evaluated sequentially, and \code{assert()} will signal
an error upon the first failed assertion, and will ignore the rest of
assertions.
}
\examples{
library(testit)
assert("T is bad for TRUE, and so is F for FALSE", {
T = FALSE
F = TRUE
(T != TRUE) # note the parentheses
(F != FALSE)
})
assert("A Poisson random number is non-negative", {
x = rpois(1, 10)
(x >= 0)
(x > -1) # () is optional because it's the last expression
})
}
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