open Reified
open Reified.Refinements
open Reified.Result
open Reified.Schema.Json

Test schema guarantees

Reified.Schema.Testing is repository tooling, not a published package. There is nothing to install. Copy or adapt the pattern shown here into your own test project.

The compiler checks type shape and visibility. It cannot prove that a constructor contains the right business rule or that a total transition preserves it.

A schema guarantee here means the behavior established by a successful Schema.parse or Schema.check call. It is not a permanent property of a public record that callers can construct elsewhere.

A transition is a function that changes one accepted domain value into another. A total transition returns the new value directly and therefore claims it cannot break the type's rules.

Use generated examples to check those claims near the owning module.

Generate accepted models

The repository contains a non-packable Reified.Schema.Testing project as a test-only FsCheck adapter. It is not published on NuGet. The example below documents the adapter used by Reified's own tests and a pattern an application can adapt locally. SchemaGen.model derives values by generating structured data, parsing it, and immediately checking the result.

open Reified.Schema.Testing
open FsCheck.FSharp

let bookingGenerator =
    SchemaGen.model Booking.schema
    |> Result.defaultWith (failwithf "%A")

let bookings = Gen.sample 100 bookingGenerator

Keep an adapter like this in test code; it is not a runtime dependency.

Check total transitions

A transition returning Booking claims it always preserves the aggregate invariant.

let shiftedBookings =
    bookings
    |> Array.map (Booking.shift 10)

let allRemainValid =
    shiftedBookings
    |> Array.forall (Schema.check Booking.schema >> Result.isOk)

Use an FsCheck property in a real test suite so it explores different values and shift amounts.

Check codecs and mappings

For generated domain values, test that serialization and decoding preserve the value expected by the application.

For wire-to-domain mappings, generate wire values and assert that accepted values produce a domain value that passes its own constructor or schema.

Do not derive all test input from the schema. Schema-derived generation is good at accepted values. Keep separate broad or hand-picked inputs for malformed data, constraint edges, and constructor failures.

Supply custom generators when needed

Patterns, custom constraints, and application-specific distributions cannot always be reversed automatically. SchemaGen.rawWith accepts generators keyed by field path.

let overrides =
    Map.ofList [ "reference", Gen.constant (Data.Text "BK-42") ]

let rawGenerator =
    SchemaGen.rawWith overrides bookingDeriveSchema
    |> Result.defaultWith (failwithf "%A")

The adapter reports UnsupportedConstraint instead of guessing a generator that might disagree with the schema.