@batterii/fake-query

@batterii/fake-query

This module exposes a fake Objection query builder for unit tests. It is built using Sinon and is intended to be used in conjunction with it.

The FakeQuery Class

A named export of this module, the FakeQuery exposes a fake QueryBuilder instance on its builder property. You can inject the fake into your code under test by stubbing the static ::query method on the desired model.

The fake builder automatically creates sinon stubs for any property accessed on the builder, except for the #then and #catch methods used to execute the query and obtain its result, as well as the #inspect method which prints out a string representation of the builder.

Created stubs always return this, as all QueryBuilder methods are chainable. Test code can examine the stubs property to write assertions about the query. Typically, you will want to do a keys assertion on the stubs object, followed by sinon assertions on the stubs themselves.

By default, the fake builder will neither resolve or reject when executed, as is normal for sinon stubs. If you want it to resolve or reject, simply involve the #resolves or #rejects methods with the desired result value.

Once the fake builder has been executed, it can no longer be changed. If any of its instance methods are invoked, or if you attempt to change its result with #resolves or #rejects, the invoked method will throw. This ensures that your assertions are always referring to the state of the builder when it was executed, and not after.

Example (Using TypeScript, Mocha, and Chai)

import {FakeQuery} from "@batterii/fake-query";
import {MyModel} from "../path/to/my-model";
import chai from "chai";
import sinon from "sinon";
import sinonChai from "sinon-chai";

chai.use(sinonChai);
const {expect} = chai;

describe('functionUnderTest', function() {
	let qry: FakeQuery;

	beforeEach(function() {
		qry = new FakeQuery();

		// Make sure this stub is cleaned up! See the `afterEach` below.
		sinon.stub(MyModel, "query").returns(qry.builder);
	});

	afterEach(function() {
		sinon.restore();
	});

	it("deletes the things", async function() {
		const deletedThings = [];
		qry.resolves(deletedThings);

		const result = await functionUnderTest();

		expect(MyModel.query).to.be.calledOnce;
		expect(MyModel.query).to.be.calledOn(MyModel);
		expect(MyModel.query).to.be.calledWithExactly();
		expect(qry.stubs).to.have.keys(["delete", "where", "returning"]);
		expect(qry.stubs.delete).to.be.calledOnce;
		expect(qry.stubs.delete).to.be.calledWithExactly();
		expect(qry.stubs.where).to.be.calledOnce;
		expect(qry.stubs.where).to.be.calledWith("id", ">", 42);
		expect(qry.stubs.returning).to.be.calledOnce;
		expect(qry.stubs.returning).to.be.calledWith("*");
		expect(result).to.equal(deletedThings);
	});
});

// Any non-cosmetic changes to this function will cause the above test to fail.
async function functionUnderTest(): Promise<MyModel[]> {
	return MyModel.query()
		.delete()
		.where('id', '>', 42)
		.returning('*');
}