Jest 21 expects result.message to always be a function

[nigelzor]

When using jest-enzyme with pre-release versions of Jest, failed assertions don't display correctly. Instead of seeing a useful description of the failed assertion, we get TypeError: message is not a function.

Returning a function remains compatible with older versions of Jest.

ref: jestjs/jest#3921
ref: jestjs/jest#3972

[blainekasten]

This looks legit! Do you know how far back this function support was introduced in jest? Just trying to think through if we should make this a major breaking change or if we can get away with a patch change here.

[nigelzor]

Just a patch, I think. The handling for function-typed message goes back to Jest 14, and expect.extend wasn't added until after that (Jest 17).

[blainekasten]

Brilliant. Thanks for the work!