test(openapi): add explicit fast-check property

Author: skulidropek

packages/app/tests/docker-git/openapi-effect-client.test.ts

@@ -1,8 +1,9 @@
 import * as Schema from "@effect/schema/Schema"
+import * as ParseResult from "@effect/schema/ParseResult"
 import { describe, expect, it } from "@effect/vitest"
 import { createClient } from "@prover-coder-ai/docker-git-openapi"
 import type { ApiTransportValue } from "@prover-coder-ai/docker-git-openapi"
-import { Effect } from "effect"
+import { Effect, Either } from "effect"
 import * as fc from "fast-check"
 
 type CapturedRequest = {
@@ -39,6 +40,25 @@ const createMockFetch = (
   return Effect.runPromise(Effect.succeed(response))
 }
 
+/**
+ * Runs a fast-check synchronous property inside the Effect test runtime.
+ *
+ * @param property - Finite pure property over OpenAPI boundary values.
+ * @returns Effect that fails when fast-check finds a counterexample.
+ *
+ * @pure false - executes property samples.
+ * @effect Effect.sync, fc.assert.
+ * @invariant success proves every sampled case preserved the asserted pure invariant.
+ * @precondition property predicate is synchronous and total.
+ * @postcondition counterexamples are surfaced through the Effect error channel.
+ * @complexity O(r * c) where r is numRuns and c is one predicate cost.
+ * @throws Never.
+ */
+const assertOpenApiClientSyncProperty = <PropertyArgs>(property: fc.IProperty<PropertyArgs>) =>
+  Effect.sync(() => {
+    fc.assert(property, { numRuns: 25 })
+  })
+
 /**
  * Runs a fast-check async property inside the Effect test runtime.
  *
@@ -91,6 +111,16 @@ describe("docker-git OpenAPI Effect client", () => {
       expect(new URL(requests[0]?.url ?? "").searchParams.has("_")).toBe(true)
     }))
 
+  it.effect("property: schema decoding preserves JSON null transport values", () =>
+    assertOpenApiClientSyncProperty(
+      fc.property(fc.constant(null), (value) =>
+        Either.match(ParseResult.decodeUnknownEither(Schema.Null)(value), {
+          onLeft: () => false,
+          onRight: (decoded) => decoded === null
+        })
+      )
+    ))
+
   it.effect("property: GET requests always include no-cache transport invariants", () =>
     assertOpenApiClientProperty(
       fc.asyncProperty(