Overview

Scriptorium.Nib.Snapshot adds snapshot testing on top of Scriptorium.Nib. On first run the snapshot is written to disk; on every subsequent run the value is serialised and compared against the stored file.

Installation

dotnet add package Scriptorium.Nib.Snapshot

How it works

1. First run — no snapshot exists yet, it is written and the test passes.
2. Subsequent runs — the value is serialised and diffed against the stored snapshot.
3. Updating — set UPDATE_SNAPSHOTS=1 and run the tests. All snapshots are rewritten.

Snapshot files live in a __snapshots__ directory next to the test file with a .snap extension.

Usage with Scriptorium.Quill

The recommended approach is ctx.snapshot — it uses the full test path as the snapshot name automatically, so snapshot names are always unique and renaming a test is enough to regenerate its snapshot:

test ("user record", fun t ->
    t.snapshot { Name = "alice"; Age = 25 }
)

// Custom serialiser
test ("DU shape", fun t ->
    t.snapshotWith (sprintf "%A", Shape.Circle 5.0)
)

Standalone usage

Without a TestContext, use Snapshot.matches directly:

test ("user snapshot", fun _ ->
    assertThat
        { Name = "alice"; Age = 25 }
        (Snapshot.matches "user snapshot")
)

The first run writes:

=== user snapshot ===
{
  "Name": "alice",
  "Age": 25
}
=== end-snapshot ===

Snapshot.matchesWith accepts a custom serialiser as the first argument:

assertThat (Shape.Circle 5.0) (Snapshot.matchesWith (sprintf "%A", "circle snapshot"))

Updating snapshots

UPDATE_SNAPSHOTS=1 dotnet fable MyApp.Tests/ --runScript

All snapshot assertions update their stored value and pass. Commit the updated .snap files.

Snapshot file format

Multiple snapshots from the same test file share one .snap file, keyed by name:

=== My suite > user snapshot ===
{
  "Name": "alice",
  "Age": 25
}
=== end-snapshot ===

=== My suite > shape snapshot ===
{
  "tag": "Circle",
  "fields": [5.0]
}
=== end-snapshot ===