testthat: use_catch – R documentation

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testthat

use_catch

Use Catch for C++ Unit Testing

Description

Add the necessary infrastructure to enable C++ unit testing in R packages with Catch and testthat.

Usage

use_catch(dir = getwd())

Arguments

dir

The directory containing an R package.

Details

Calling use_catch() will:

Create a file src/test-runner.cpp, which ensures that the testthat package will understand how to run your package's unit tests,
Create an example test file src/test-example.cpp, which showcases how you might use Catch to write a unit test,
Add a test file tests/testthat/test-cpp.R, which ensures that testthat will run your compiled tests during invocations of devtools::test() or R CMD check, and
Create a file R/catch-routine-registration.R, which ensures that R will automatically register this routine when tools::package_native_routine_registration_skeleton() is invoked.

You will also need to:

Add xml2 to Suggests, with e.g. usethis::use_package("xml2", "Suggests")
Add testthat to LinkingTo, with e.g. usethis::use_package("testthat", "LinkingTo")

C++ unit tests can be added to C++ source files within the src directory of your package, with a format similar to R code tested with testthat. Here's a simple example of a unit test written with testthat + Catch:

context("C++ Unit Test") {
  test_that("two plus two is four") {
    int result = 2 + 2;
    expect_true(result == 4);
  }
}

When your package is compiled, unit tests alongside a harness for running these tests will be compiled into your R package, with the C entry point run_testthat_tests(). testthat will use that entry point to run your unit tests when detected.

Functions

All of the functions provided by Catch are available with the CATCH_ prefix – see here for a full list. testthat provides the following wrappers, to conform with testthat's R interface:

Function	Catch	Description
`context`	`CATCH_TEST_CASE`	The context of a set of tests.
`test_that`	`CATCH_SECTION`	A test section.
`expect_true`	`CATCH_CHECK`	Test that an expression evaluates to `true`.
`expect_false`	`CATCH_CHECK_FALSE`	Test that an expression evalutes to `false`.
`expect_error`	`CATCH_CHECK_THROWS`	Test that evaluation of an expression throws an exception.
`expect_error_as`	`CATCH_CHECK_THROWS_AS`	Test that evaluation of an expression throws an exception of a specific class.

In general, you should prefer using the testthat wrappers, as testthat also does some work to ensure that any unit tests within will not be compiled or run when using the Solaris Studio compilers (as these are currently unsupported by Catch). This should make it easier to submit packages to CRAN that use Catch.

Symbol Registration

If you've opted to disable dynamic symbol lookup in your package, then you'll need to explicitly export a symbol in your package that testthat can use to run your unit tests. testthat will look for a routine with one of the names:

C_run_testthat_tests
    c_run_testthat_tests
    run_testthat_tests

See Controlling Visibility and Registering Symbols in the Writing R Extensions manual for more information.

Advanced Usage

If you'd like to write your own Catch test runner, you can instead use the testthat::catchSession() object in a file with the form:

#define TESTTHAT_TEST_RUNNER
#include <testthat.h>

void run()
{
    Catch::Session& session = testthat::catchSession();
    // interact with the session object as desired
}

This can be useful if you'd like to run your unit tests with custom arguments passed to the Catch session.

Standalone Usage

If you'd like to use the C++ unit testing facilities provided by Catch, but would prefer not to use the regular testthat R testing infrastructure, you can manually run the unit tests by inserting a call to:

.Call("run_testthat_tests", PACKAGE = <pkgName>)

as necessary within your unit test suite.