[Vuejs]-Shallow mounting in Vue, stubs not working

This took me ages to understand but I eventually see what you mean by the comments on the question.

For me this was that I needed to set an environment variable as one of my modules was expecting to reference a value that did not exist.

This is checked when the Import command is run even if when you come to mount your component the import would not be required due to some form of test double.

This is probably because Jest doesn’t know what the relation between picture-comp and PictureComp is. If this even works in Vue, then my guess is that Vue knows how to resolve kebab-case to PascalCase.
At any rate, I would expect it to work if you register the component correctly:

components: {
  'picture-comp': PictureComp
}

or, use <PictureComp> instead of <picture-comp> in your template.