No offense, but I feel like this is not a good example to follow.
The first examples are better off with just using snapshots. Even if the author is trying to explain the concepts, it is really poor to show bad examples that could be covered by a simpler solution. If I read that and didn't know about snapshots, I'd think to myself, "why am I testing strings?" and then skip testing entirely.
Mocking Axios also seems like the wrong way to approach things. I'd extract the networking code from the presentation code. Possibly by using mobx-state-tree (which is an epic solution to a hard problem). This way, I wouldn't even need to mock Axios at all and I could then just take advantage of snapshots again by providing actual mock data to my components directly.
