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I thought it was about empty strings... Going to check that

The article only considers quoted arguments. Quoting should be recommended for test, and OP probably even has a formal check for quotes being in place. However, let's just set that aside for now. Quotes are optional. And if you don't put quotes, then yes, you need to use `[ x$var = xval ]` to address empty variables.

I wonder what happens when $var starts with ‘-‘, it wouldn’t surprise me if it’s taken as an option.

It's time to read the article.

Ah, upon rereading it turns out it is still an issue:

... would fail to run test commands whose left-hand side matched a unary operator.

This was fixed [...] in 1979. However, test and [ were also available as separate executables, and appear to have retained a variant of the buggy behavior:

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