Testing is important. Most of the large companies test their software. Small companies tend to do it less though it really becomes a thing in front-end development.
Same for accessibility.
While performance is also important for an app, I think that we won't expect a beginner developer to know how to optimize an app from A to Z, some basics would do it (reducing images sizes maybe code-splitting?)
Same for SEO. It's also common in large companies to have web analysts that will cover SEO for you.
Note that it also depends on the company's technical values. Some teams really like to test extensively their code while others prefer to have a perfectly accessible app (for product needs for example). It's a thing you have to keep in mind when applying.
TL;DR: focus first on testing and accessibility. Then, tackle performance and SEO.
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Note that it also depends on the company's technical values. Some teams really like to test extensively their code while others prefer to have a perfectly accessible app (for product needs for example). It's a thing you have to keep in mind when applying.
TL;DR: focus first on testing and accessibility. Then, tackle performance and SEO.