beeler•2w ago

Basic Mocking example for `override global or imported objects` does not work

I am following the example https://docs.deno.com/examples/testing_tutorial/#basic-mocking and when run with deno test --no-check the example fails with:

getUserDetails formats the name correctly => ./service_test.ts:5:6
error: TypeError: Cannot assign to read only property 'getUserFromDB' of object '[object Module]'
  db.getUserFromDB = async (id: string) => {
                  ^
    at file:///home/.../service_test.ts:10:19

getUserDetails formats the name correctly => ./service_test.ts:5:6
error: TypeError: Cannot assign to read only property 'getUserFromDB' of object '[object Module]'
  db.getUserFromDB = async (id: string) => {
                  ^
    at file:///home/.../service_test.ts:10:19

I'm running with --no-checks to prove its not only a type issue, but the type checker does catch it if you remove the --no-check flag. Is there anyway to get this example to work or another way to isolate imports in Deno? I am using the latest Deno:

$ deno --version
deno 2.2.10 (stable, release, x86_64-unknown-linux-gnu)
v8 13.5.212.10-rusty
typescript 5.7.3

$ deno --version
deno 2.2.10 (stable, release, x86_64-unknown-linux-gnu)
v8 13.5.212.10-rusty
typescript 5.7.3

3 Replies

marvinh.•2w ago

good catch, looks like this example in the documentation is wrong. Module exports cannot be mocked as they are not writable

marvinh.•2w ago

Filed an issue for that https://github.com/denoland/docs/issues/1631

GitHub

Bug: Basic mocking example doesn't work · Issue #1631 · denoland/...

The example for basic mocking doesn't work, see https://docs.deno.com/examples/testing_tutorial/#basic-mocking . Reason it doesn't work is that it tries to replace properties of a module re...

beelerOP•2w ago

Thank you for opening the issue. I'll look around to see how people handle breaking dependencies.

Basic Mocking example for `override global or imported objects` does not work

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