Json-schema-fast-check NPM

json-schema-fast-check

JSON Schema is a useful way to define input and output schemas.

Property testing is a useful way to make sure that a function behaves as expected with any valid input.

json-schema-fast-check implements arbitrary JSON Schema values using the fast-check library for property testing.

Example

import jsfc from "json-schema-fast-check";
import fc from "fast-check";

const getAge = (data: any) =>
    typeof data === "object" && typeof data.age === "number"
    ? Math.floor(data.age)
    : null;

const userSchema = {
    type: "object",
    properties: {
        required: ["name", "id"],
        name: {
            type: "string"
        },
        age: {
            type: "integer",
            minimum: 0
        },
        id: {
            type: "integer"
        }
    }
}

test("my function yields positive age or null", () => {
    fc.assert(fc.property(jsfc(userSchema), user => {
        const age = getAge(user);
        return age === null || age >= 0;
    }));
});

API

The API has only two functions - the default one (which we call jsfc just cuz) and a helper function called generate.

`jsfc` (default)

const arbitrary = jsfc(mySchema);

Creates a fast-check arbitrary from valid JSON schema.

`generate`

const json = generate(mySchema);

Generates a single valid JSON object that conforms to the schema.

A note on JSON Schema

The actual schema used here is not JSON Schema but rather a subset of JSON Schema called "The Subest of JSON Schema I Was Not Too Lazy To Define." I also added some faker-js sugar (see the tests).