The solution to "Error handling"...

[Walter Bright]

On 7/9/2026 12:32 AM, Robert Collins wrote:
> Instead of 
> only catching exceptions, we started testing common failure scenarios such as 
> invalid input, missing resources, API timeouts, and permission issues. We also 
> separated user-friendly messages from detailed logs, so users received clear 
> guidance while developers still had enough information to troubleshoot the root 
> cause.

One testing technique that works well is to have input objects, processing code, 
and output objects. One creates "mock" input objects, which can be used to 
generate specific bad input. Then write "mock" output objects that, instead of 
reporting the error, compare the error against what the expected error would be.

You can see this in action in the lexer unittests in the dmd compiler.