Interactive Snapshot Testing — snapshot • resultcheck

Creates or updates a snapshot of an R object for interactive analysis. On first use, saves the object to a human-readable snapshot file (.md). On subsequent uses, compares the current object to the saved snapshot.

Usage

snapshot(value, name, script_name = NULL, method = NULL)

Arguments

value: The R object to snapshot (e.g., plot, table, model output).
name: Character. A descriptive name for this snapshot.
script_name: Optional. The name of the script creating the snapshot. If NULL, auto-detects via rstudioapi::getSourceEditorContext()$path (in RStudio), falling back to the call stack, then to "interactive".
method: Optional function or non-empty list of functions used to serialize value. Functions are executed in order and each section header is taken from the method expression or list name. If omitted, method defaults are resolved in this order: snapshot.method_by_class (matched by object class), then snapshot.method, then list(print = base::print, str = utils::str).

Value

Invisible TRUE if snapshot matches or was updated. In testing mode, throws an error if snapshot is missing or doesn't match.

Details

In interactive mode (default), prompts the user to update if differences are found and emits a warning. In testing mode (inside testthat or run_in_sandbox), throws an error if snapshot doesn't exist or doesn't match.

Snapshots are stored under tests/_resultcheck_snaps/ by default, organized by script name, and configurable via snapshot.dir in _resultcheck.yml. Method defaults can be configured via snapshot.method and class-specific defaults via snapshot.method_by_class. Optional class defaults can also be loaded from an R file using snapshot.method_defaults_file. Method strings in config (for example "print + str" or "stats::coef") are resolved to callable functions. In config expressions, "+" is treated as the method delimiter.

Built-in class defaults (loaded from inst/extdata/snapshot-method-defaults.R) use broom functions for many statistical model classes. The default method is typically broom::tidy, with broom::glance and/or broom::augment added where supported (per the broom available-methods table at https://broom.tidymodels.org/articles/available-methods.html).

Examples

with_example({
  model <- stats::lm(mpg ~ wt, data = datasets::mtcars)
  snapshot(model, "model_default", script_name = "analysis")
  snapshot(model, "model_multi", script_name = "analysis",
           method = list(summary = summary, print = print))
  snapshot(model, "model_print", script_name = "analysis", method = print)
  snapshot(model, "model_ns", script_name = "analysis", method = stats::coef)
  snapshot(model, "model_length", script_name = "analysis", method = length)
})
#> ✓ New snapshot saved: analysis/model_default.md
#> ✓ New snapshot saved: analysis/model_multi.md
#> ✓ New snapshot saved: analysis/model_print.md
#> ✓ New snapshot saved: analysis/model_ns.md
#> ✓ New snapshot saved: analysis/model_length.md

with_example({
  sandbox <- setup_sandbox()
  on.exit(cleanup_sandbox(sandbox), add = TRUE)
  run_in_sandbox("analysis.R", sandbox)
})

if (interactive()) with_example({
  sandbox <- setup_sandbox()
  on.exit(cleanup_sandbox(sandbox), add = TRUE)
  run_in_sandbox("analysis.R", sandbox)
}, mismatch = TRUE)