Throw when mount/shallow rendering invalid root elements

[jgzuke]

Throw TypeError('ShallowWrapper can only wrap valid elements') or TypeError('ReactWrapper can only wrap valid elements') when ShallowWrapper or ReactWrapper are created wrapping an invalid element as root.

[ljharb]

Thanks, this looks great!

[ljharb]

This will actually need a rebase

[ljharb]

hmm, nodes could be an array of valid elements; i'm not sure we can check it directly.

also, i think we probably want to check this on root too if that's provided?

[jgzuke]

I think if we try to mount an array of elements as the root that should still throw.

root elements should always have already been through this path when they were created, ie wrap/ReactWrapper constructor only get called with null when mounting (or diving in the shallow wrapper) or this[ROOT] when traversing, which is only set here.

[jgzuke]

The tests added failed previously with

AssertionError: expected [Function] to throw 'TypeError' but 'Invariant Violation: Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: undefined. You likely forgot to export your component from the file it\'s defined in, or you might have mixed up default and named imports.\n\nCheck the render method of `WrapperComponent`.' was thrown
+ expected - actual

-Invariant Violation: Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: undefined. You likely forgot to export your component from the file it's defined in, or you might have mixed up default and named imports.
-
-Check the render method of `WrapperComponent`.
+TypeError

at Context.<anonymous> (packages/enzyme-test-suite/test/ReactWrapper-spec.jsx:94:7)

for the mount tests and

AssertionError: expected [Function] to throw 'TypeError' but 'Invariant Violation: Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: undefined. You likely forgot to export your component from the file it\'s defined in, or you might have mixed up default and named imports.\n\nCheck the render method of `WrapperComponent`.' was thrown
+ expected - actual

-Invariant Violation: Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: undefined. You likely forgot to export your component from the file it's defined in, or you might have mixed up default and named imports.
-
-Check the render method of `WrapperComponent`.
+TypeError

at Context.<anonymous> (packages/enzyme-test-suite/test/ReactWrapper-spec.jsx:101:7)

for the shallow tests