In bug 1296397, I ran into issues where WPT was running in automation without a loaded mozinfo.json because the path to mozinfo.json changed. This caused a number of head-scratching test failures because it wasn't obvious that mozinfo.json wasn't loaded. The code in mozinfo.find_and_update_from_json() currently no-ops if no mozinfo.json could be loaded. Since mozinfo.json is kinda critical to ensure tests run properly, we should consider changing it to fail if it can't find a mozinfo.json. Alternatively, callers of this function relying on a mozinfo.json (such as automation) should raise if it returns None.
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