roblox-ts•2mo ago

How to mock a library function in jest

I tried doing .spyOn to spy on the function but it didn't work. I don't think .mock works because it requires a module script, and roblox-ts strings will mess up its mockings

13 Replies

duckOP•2mo ago

in my use case, I tried mocking matter's useDeltaTime function to return a deseried delta time value, but I can't find out how to do that

iSentinel•2mo ago

You need to dynamically import I did something like:

export function mockPlayerService(players?: Array<Player>): {
    onPlayerAdded: Signal<(player: Player) => void>;
    onPlayerRemoved: Signal<(player: Player) => void>;
} {
    const onPlayerAdded = new Signal<(player: Player) => void>();
    const onPlayerRemoved = new Signal<(player: Player) => void>();

    jest.mock(getServices(), () => {
        return {
            Players: {
                GetPlayerByUserId(userId: number): Player | undefined {
                    return players?.find(player => player.UserId === userId);
                },
                GetPlayers: () => players ?? [],
                PlayerAdded: onPlayerAdded,
                PlayerRemoving: onPlayerRemoved,
            },
            RunService: {
                IsServer: () => game.GetService("RunService").IsServer(),
                IsStudio: () => game.GetService("RunService").IsStudio(),
            },
        };
    });

    return { onPlayerAdded, onPlayerRemoved };
}

export function mockPlayerService(players?: Array<Player>): {
    onPlayerAdded: Signal<(player: Player) => void>;
    onPlayerRemoved: Signal<(player: Player) => void>;
} {
    const onPlayerAdded = new Signal<(player: Player) => void>();
    const onPlayerRemoved = new Signal<(player: Player) => void>();

    jest.mock(getServices(), () => {
        return {
            Players: {
                GetPlayerByUserId(userId: number): Player | undefined {
                    return players?.find(player => player.UserId === userId);
                },
                GetPlayers: () => players ?? [],
                PlayerAdded: onPlayerAdded,
                PlayerRemoving: onPlayerRemoved,
            },
            RunService: {
                IsServer: () => game.GetService("RunService").IsServer(),
                IsStudio: () => game.GetService("RunService").IsStudio(),
            },
        };
    });

    return { onPlayerAdded, onPlayerRemoved };
}

and then my code looked like:

describe("a test", () => {
    let someFileThatImportsPlayerService: Example;

    beforeEach(() => {
        const { Example } = import("path/to/some-file-that-imports-player-service").expect();
            someFileThatImportsPlayerService = Example;    
    });

describe("a test", () => {
    let someFileThatImportsPlayerService: Example;

    beforeEach(() => {
        const { Example } = import("path/to/some-file-that-imports-player-service").expect();
            someFileThatImportsPlayerService = Example;    
    });

you need to ensure you mock it before you import it

duckOP•2mo ago

what is getServices?

lisachandra•2mo ago

just mock the module that exports getdeltatime no?

const useDeltaTimeMock = jest.fn()
beforeAll(() => {
    const useDeltaTimeModule = getModuleByTree(...$getModuleTree("@rbxts/matter/lib/hooks/useDeltaTime"))
    jest.mock<typeof import("@rbxts/matter/lib/hooks/useDeltaTime")>(useDeltaTimeModule, () => {
        return useDeltaTimeMock;
    })
})

const useDeltaTimeMock = jest.fn()
beforeAll(() => {
    const useDeltaTimeModule = getModuleByTree(...$getModuleTree("@rbxts/matter/lib/hooks/useDeltaTime"))
    jest.mock<typeof import("@rbxts/matter/lib/hooks/useDeltaTime")>(useDeltaTimeModule, () => {
        return useDeltaTimeMock;
    })
})

make sure the mock is setup before importing anything else that might import matter aswell

iSentinel•2mo ago

it was just

export function getServices(): ModuleScript {
    return ReplicatedStorage.rbxts_include
        .FindFirstChild("node_modules")
        ?.FindFirstChild("@rbxts")
        ?.FindFirstChild("services") as ModuleScript;
}

export function getServices(): ModuleScript {
    return ReplicatedStorage.rbxts_include
        .FindFirstChild("node_modules")
        ?.FindFirstChild("@rbxts")
        ?.FindFirstChild("services") as ModuleScript;
}

duckOP•2mo ago

        const func = jest.fn();

        const useDeltaTimeMock = jest.mock<
            typeof import("@rbxts/planck-matter-hooks/out/hooks/useDeltaTime")
        >(
            getModuleByTree(...$getModuleTree("@rbxts/planck-matter-hooks/out/hooks/useDeltaTime")),
            () => ({ useDeltaTime: func() }),
        );

        func.mockReturnValue(0);

        print(useDeltaTime());

        const func = jest.fn();

        const useDeltaTimeMock = jest.mock<
            typeof import("@rbxts/planck-matter-hooks/out/hooks/useDeltaTime")
        >(
            getModuleByTree(...$getModuleTree("@rbxts/planck-matter-hooks/out/hooks/useDeltaTime")),
            () => ({ useDeltaTime: func() }),
        );

        func.mockReturnValue(0);

        print(useDeltaTime());