dependencies are duplicated for each test file

[LarsDenBakker]

Each test file is treated as a separate bundle. Common dependencies are duplicated between the test files.

This is wasteful, and creates extra overhead for large project. But more importantly it creates issues when working with web components, as they may only be registered once per document. Bundling the same web component twice will throw an error.

I creates a reproduction for this: https://github.com/LarsDenBakker/karma-rollup-preprocessor-issues

npm install
npm run test:dynamic-import
optionally, debug the code at: http://localhost:9876/debug.html

You will see the error being thrown. If you inspect the output bundles in the browser, you will see the web component code bundled twice.

We are switching from webpack to rollup for our recommended setup for developers working with web component at: https://open-wc.org/

We had a similar issue with webpack codymikol/karma-webpack#379 which we were able to solve.

Happy to help out where possible.

[AgDude]

This issue also makes debugging tests in a browser very difficult. Since the source is duplicated, sourcemaps are unreliable, making it is difficult to put breakpoints in the right place.

[AgDude]

I am able to mostly avoid this problem by creating a single entry point for tests.

Create an entry point like: find src -name '*.spec.js' | awk '{print "export * from '\''./" $0 "'\'';"}' > karma-entry.spec.js

Then instead of including /src/**/*.js include only karma-entry.spec.js

It would be nice if the preprocessor could handle this automatically, but incorporating this in our npm script seems to solve the problem for us.

[tommck]

Wow.. I wish I had realized this before I converted by old webpack build to rollup. This also makes testing incredibly slow! It's honestly unusable in its current state :(

[Lalem001]

@tommck The problem is in Karma, not Rollup (or karma-rollup-preprocessor). If you see Karma Webpack's Alternative Usage section, it too suggests a single entry point referencing all other files for more performance.

[tommck]

@Lalem001 and ... rollup doesn't support importing a bunch of test files all into one in a simple way like webpack does. So... rollup doesn't have any built-in way to mitigate this. I'd say that's still a rollup + karma problem, since it's solved w/ webpack

[Lalem001]

@tommck

rollup doesn't support importing a bunch of test files all into one

Officially, it does. See @rollup/plugin-multi-entry

I'd say that's still a rollup + karma problem, since it's solved w/ webpack

Webpack + Karma has the same problems as rollup + karma. The link I posted in my previous comment talks about this. Karma forces Webpack/Rollup to generate a bundle for EACH test. The way around it, the "alternative usage", is to have a single entry file that imports all other tests.

[tommck]

And webpack makes it easier to have that single point of entry. Neither rollup nor this plugin has any solution for the problem. It's disappointing.

…

On Mon, Mar 16, 2020, 4:29 PM Luis Aleman ***@***.***> wrote: rollup doesn't support importing a bunch of test files all into one Officially, it does. See @rollup/plugin-multi-entry <https://github.com/rollup/plugins/tree/master/packages/multi-entry> I'd say that's still a rollup + karma problem, since it's solved w/ webpack Webpack + Karma has the same problems as rollup + karma. The link I posted in my previous comment talks about this. Karma forces Webpack/Rollup to generate a bundle for EACH test. The way around it, the "alternative usage", is to have a single entry file that imports all other tests. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#49 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAHPXRJAK6TN2SUFYJMT4BLRH2D37ANCNFSM4G42PPGQ> .

[tommck]

@Lalem001 multiple entry points is exactly the OPPOSITE if what we need here. We need 1 entry point that pulls in all spec files so that it's ONE bundle

[Lalem001]

@tommck I know, and that is what I suggested above. A single entry point that imports all others.

[tommck]

...which we have to create manually

[Lalem001]

@tommck Not necessarily. Like webpack (webpack-import-glob-loader), Rollup can be configured to import with glob (rollup-plugin-glob-import).

In which case you could have your entry file look like the following:

import '**/*.spec.js';

Please pay attention to the fact that Webpack too must be configured to work this way, which is what I have been saying all along. Webpack faces the same issues as Rollup when it comes to working within the confines of Karma. Fixing this issue requires changes to Karma itself.

[jlmakes]

I'd like to drop support for Rollup@1 and Node@8 and release 8.0.0, which will be a great opportunity to update this library's documentation to help with this situation. Any suggestions?

[Lalem001]

Honestly, just a section similar to the one in Karma Webpack's readme would suffice. Single entry does come with caveats in my experience though. Karma watcher doesn't really work since it is only working with a single file. And the glob import scripts linked above do not see high amounts of usage.