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Learn how to conditionally execute `npm run test` using `lerna exec` with this simple guide.
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This video is based on the question https://stackoverflow.com/q/63930897/ asked by the user 'Lannnn' ( https://stackoverflow.com/u/10959622/ ) and on the answer https://stackoverflow.com/a/63932141/ provided by the user 'Digvijay S' ( https://stackoverflow.com/u/12991188/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Mastering Conditional npm run test with lerna exec

When working with multiple packages in a JavaScript project, managing tests can become a bit cumbersome. Especially if you want to run tests only under certain conditions. If you've found yourself in this scenario, you might be wondering how to effectively run npm run test using lerna exec based on specific criteria. In this guide, we'll explore how to achieve this seamlessly.

The Problem at Hand

You may have a requirement to run tests only when certain patterns are matched in the output of a command. For instance:

[[See Video to Reveal this Text or Code Snippet]]

While the above command tries to execute npm run test conditionally, it can be simplified for better performance and clarity.

The Solution: Simplifying the Command

To ensure npm run test only runs when the conditions are true, we can utilize the grep command. Here’s the revised command you'll want to use:

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Breakdown of the Solution

Using lerna exec: This command allows the execution of scripts across the packages managed by Lerna. We specify concurrency and scope to control how the command runs.

The Output Command: Instead of using awk, we pipe the output to grep. This provides a cleaner and more efficient way to check if a particular pattern exists in the output.

Conditionally Running the Test:

grep '<pattern match>': Checks if the output contains the specified pattern.

&& npm run test: This ensures that npm run test executes only if the previous command (the grep command) is successful—that is, the pattern is matched.

Example in Action

To further illustrate this, let’s take a look at a practical example:

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Output:

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In this demo:

The first echo command does not contain numbers, so "Yes" is not printed.

The second command successfully matches the pattern and prints "Yes".

Conclusion

By following the simplified command structure, you can efficiently run your tests conditionally when using Lerna. This approach not only streamlines the process but also makes your scripts easier to read and maintain.

In summary, applying lerna exec with a combination of grep and conditional execution can vastly improve how you manage tests in multi-package projects. Happy coding!