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4 months ago
21
May 28, 2025
Zürich, SchweizToday, driven by annoyance, I refactor-extracted a small set of test helper code found in various private personal projects around the topic of golden file management into a dedicated Go module: github.com/matttproud/goldentest (API documentation). I’m happy to finally have a canonical solution that I am happy with.
I’ll freely admit it: I use change detector tests1 for some things, as a slew of these personal projects use reference data defined in the testdata directory as canonical want values that got is compared against. It’s practical: for code that generates HTML files, I can inspect the files in a browser or local web server and verify behavior conformance. Same goes for end-to-end tests that generate output. In select cases, it is easier than redefining onerous data literals in my test themselves — not that I like indirection all that much.
So what compelled me to have written my own testing helpers around golden files? It’s rather simple: I found the existing solutions not particularly idiomatic; and I don’t say that to chide any of them.
Long story short: I wanted a small, minimalist, and opinionated framework for checking whether data values generated by a system under test (SUT) match reference values.
By “minimalist” and “opinionated,” I want something that is:
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Effectively the spiritual companion to package cmp but for management of files in the testdata directory.
It does relatively little but is extensible (see the package’s example to see what I mean by extensibility); I have this library even driving an image diffing protocol that works with external viewer tools
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Conformant with prevailing Go style guidelines whereby the diffing mechanisms do not act as assertions. They merely present a diff and update the reference values in the testdata directory.
Anyway, perhaps this library is useful to you. I’ve converted seven projects over to it, so I’ll consider it a win.
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