Meziantou.Framework

Snapshot types

edit

A SnapshotType gives the format of a snapshot: the extension of its file and, for some serializers, how the value is written. Without a type, a value is stored as text (SnapshotType.Default, a .txt file).

Validate a file in its own format

Pass the type after the value. A string is stored as it is, a byte[] or a Stream is stored as its bytes:

var imageBytes = Convert.FromBase64String("iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAIAAACQd1PeAAAADElEQVR4nGP4z8AAAAMBAQDJ/pLvAAAAAElFTkSuQmCC"); // A 1x1 PNG image
var svgText = """<svg xmlns="http://www.w3.org/2000/svg" width="10" height="10"><rect width="10" height="10" fill="red" /></svg>""";

Snapshot.Validate(imageBytes, SnapshotType.Png);
Snapshot.Validate(svgText, SnapshotType.Svg);

To read a Stream asynchronously, use Snapshot.ValidateAsync, see Asynchronous values.

A type also converts from a string, which is the extension of the file: Snapshot.Validate(spec, "yaml") stores a .yaml file. SnapshotType.Create("cs") does the same, and SnapshotType.Create(type, mimeType, displayName) also sets the MimeType and DisplayName of the type. A leading dot is ignored, and jpg and tif are the same types as jpeg and tiff.

The built-in types are Default (txt), Svg, Png, Bmp, Jpeg, Tiff, Webp, Gif, Ico, Avif, Heic, JpegXl (jxl), Jpeg2000 (jp2), Pdf, and None, a snapshot without a format, stored as a .bin file.

How each format is compared

  • Text formats are compared without regard to line endings: \r\n, \r and \n are equivalent, and a leading UTF-8 byte order mark is ignored. A verified file whose line endings were changed by an editor, a merge tool or git still matches. This applies to every known text format: txt, json, yaml, xml, html, svg, md, csv, cs, vb, razor, sql, and their common variants. A compound extension is classified by its last segment, so g.cs and d.ts are text formats.
  • Other formats, such as png, pdf, bin or tar.gz, are compared byte for byte.

A comparer registered for a format replaces this behavior. Image formats are compared byte for byte unless you register the image comparer of Meziantou.Framework.SnapshotTesting.Imaging, which compares their pixels; PDF documents are compared page by page with Meziantou.Framework.SnapshotTesting.Pdf. See Extensions and Serializers and comparers.

Text and binary snapshots

Scrubbers, which remove unstable values from a snapshot (see Deterministic snapshots), only apply to text snapshots. A snapshot in a known binary format (png, jpeg, pdf, zip, bin, ...) is never scrubbed, even when its bytes happen to be valid UTF-8. A snapshot in an unknown format is scrubbed when its content is UTF-8 text.