Verify

Verify (by Simon Cropp) is the most widely used snapshot testing library for .NET. It serializes the result of a test to a .received. file, compares it against a committed .verified. snapshot, and fails the test when they diverge — ideal for asserting complex object graphs, HTTP responses, generated code, and documents. It ships integrations for xUnit v3, NUnit, MSTest, TUnit, Fixie, and Expecto, and the source is MIT-licensed.

In August 2026 (VerifyTests/discussions#1731) Simon Cropp announced that Verify is adopting the Open Source Maintenance Fee (OSMF) model, with a build-time sponsorship check from v33 onward.

What Changed

The source stays MIT and freely available. As Simon Cropp put it:

"The ongoing work of maintaining Verify … takes real, sustained effort. The Maintenance Fee model is one way to make that work more sustainable."

Two things are new:

1. Package license (OsmfEula.txt). Every version released after 1 September 2026 carries an OSMF EULA on the compiled binaries. Versions released on or before that date are unaffected. The EULA does not restrict self-compiled binaries or forks.
2. Build-time enforcement via SponsorCheck. From v33, Verify validates sponsorship locally at build time (no network calls). An organization declares its GitHub Sponsors account once in a project property, covering every Verify package in the repo. An escape hatch — <SponsorshipLicenseIgnored>true</SponsorshipLicenseIgnored> — prevents a false negative from blocking work.

This is a stricter posture than the purely contractual approach taken by Polly or NPOI.

Who Pays and How Much

Paid via GitHub Sponsors (monthly or annual, invoicing available), tiered by organization size — deliberately set below the standard OSMF recommendation:

• Small (< 40 employees): $5/month
• Medium (40–200 employees): $20/month
• Large (200–1,000 employees): $30/month
• Enterprise (> 1,000 employees): $100/month

Who must pay: organizations with annual gross revenue of at least US $10,000 that use Verify in revenue-generating activity, plus all government agencies.

Exempt: individuals, non-revenue organizations, forks, contributions, and local development.

What This Means For You

• Individual / OSS / non-revenue: nothing to do. Set SponsorshipLicenseIgnored if the build check trips.
• Company under $10k revenue: exempt, but the v33+ build check may need the escape-hatch property.
• Company over $10k revenue: sponsor VerifyTests at your tier and set the GitHub Sponsors account property, or stay on a version released on/before 1 September 2026.
• Government agency: the fee applies regardless of revenue.

Alternatives

1. Pin Verify to a pre-OSMF version:

   • Anything released on or before 1 September 2026 (pre-v33) has no EULA and no SponsorCheck.
   • Pros: zero migration, still MIT.
   • Cons: no future fixes, framework updates, or new serializer features.

2. Snapshooter (SwissLife-OSS):

   • Jest-inspired snapshot testing for .NET, MIT-licensed, actively maintained. Supports xUnit, NUnit, and MSTest. API: Snapshot.Match(result); with field-ignore, hashing, and inline field assertions.
   • Pros: free, closest feature match, simple API.
   • Cons: smaller ecosystem than Verify; fewer built-in serialization modules (EF, HTTP, etc.); no xUnit v3 / TUnit parity.

3. ApprovalTests.Net:

   • The original .NET approval-testing library (Verify itself grew out of this lineage). MIT-ish (Apache-2.0).
   • Pros: free, mature, reporter/diff-tool ecosystem, many framework adapters.
   • Cons: more manual configuration; serialization is less batteries-included than Verify.

4. Build your own with System.Text.Json + file compare:

   • For simple DTO snapshots: serialize, write *.received.json, diff against a committed *.verified.json, fail on mismatch (~30 lines of helper).
   • Cons: you reimplement scrubbing, diff-tool launching, directory conventions, and pretty-printing that Verify gives you for free.

5. Move assertions to explicit Assert / Shouldly / Awesome Assertions:

   • Where a snapshot was really just asserting a handful of fields, an explicit assertion is clearer and dependency-free.
   • Cons: not viable for large payloads or generated-output tests, which is exactly where Verify shines.

Conclusion

Verify's source remains MIT, but versions after 1 September 2026 (v33+) attach an OSMF EULA and a local build-time SponsorCheck. Revenue-generating organizations above $10k — and every government agency — are expected to sponsor VerifyTests at $5–$100/month by tier. Individuals and non-revenue users stay free (with an escape-hatch property). Teams that prefer not to engage can pin to a pre-v33 release or move to MIT-licensed Snapshooter or ApprovalTests.Net.

Links and References

• GitHub Discussion: Open Source Maintenance Fee (VerifyTests/discussions#1731)
• GitHub: VerifyTests/Verify
• GitHub: SimonCropp/SponsorCheck · Consumer usage guide
• GitHub Sponsors: VerifyTests
• Open Source Maintenance Fee: Home · FAQ
• Alternative: Snapshooter
• Alternative: ApprovalTests.Net
• Similar model: Polly · json-everything · NPOI