expect_snapshot_output: Snapshot helpers

Description

These snapshotting functions are questioning because they were developed before expect_snapshot() and we're not sure that they still have a role to play.

expect_snapshot_output() captures just output printed to the console.
expect_snapshot_error() captures an error message and optionally checks its class.
expect_snapshot_warning() captures a warning message and optionally checks its class.

Usage

expect_snapshot_output(x, cran = FALSE, variant = NULL)
expect_snapshot_error(x, class = "error", cran = FALSE, variant = NULL)
expect_snapshot_warning(x, class = "warning", cran = FALSE, variant = NULL)

Arguments

x

Code to evaluate.

cran

Should these expectations be verified on CRAN? By default, they are not, because snapshot tests tend to be fragile because they often rely on minor details of dependencies.

variant

If non-NULL, results will be saved in _snaps/{variant}/{test.md}, so variant must be a single string suitable for use as a directory name.

You can use variants to deal with cases where the snapshot output varies and you want to capture and test the variations. Common use cases include variations for operating system, R version, or version of key dependency. Variants are an advanced feature. When you use them, you'll need to carefully think about your testing strategy to ensure that all important variants are covered by automated tests, and ensure that you have a way to get snapshot changes out of your CI system and back into the repo.

class

Class of expected error or warning. The expectation will always fail (even on CRAN) if an error of this class isn't seen when executing x.