Add failing test showing splitBlock with isVoid bug (#276)

* Add failing test showing splitBlock with isVoid bug

Not sure what I actually expected calling `splitBlock()` on void block, but I
would expect `splitBlock()` to respect a given block type's isVoid property.
This failing test demonstrates that `splitBlock()` always creates a the new
block with `isVoid: false`.

* Fix isVoid not being copied when using splitBlock()

The bug was actually inside `splitBlockAtRange`, as that's what actual drives
`splitBlock()` (I assume the bug was therefore present in both methods). The
fix is to simply copy across the `isVoid` value from the block being copied.

lib/models/transforms.js

@@ -612,7 +612,8 @@ const Transforms = {
       secondChild = Block.create({
         nodes: secondChildren,
         type: parent.type,
-        data: parent.data
+        data: parent.data,
+        isVoid: parent.isVoid
       })
 
       // Add the new children.

test/transforms/fixtures/split-block/with-void/index.js

@@ -0,0 +1,24 @@
+
+import assert from 'assert'
+
+export default function (state) {
+  const { document, selection } = state
+  const texts = document.getTexts()
+  const first = texts.first()
+  const range = selection.merge({
+    anchorKey: first.key,
+    anchorOffset: 0,
+    focusKey: first.key,
+    focusOffset: 0
+  })
+
+  const next = state
+    .transform()
+    .moveTo(range)
+    .splitBlock()
+    .apply()
+
+  console.dir(next.document.getBlocks().toJS());
+
+  return next
+}

test/transforms/fixtures/split-block/with-void/input.yaml

@@ -0,0 +1,5 @@
+
+nodes:
+  - kind: block
+    type: video
+    isVoid: true

test/transforms/fixtures/split-block/with-void/output.yaml

@@ -0,0 +1,8 @@
+
+nodes:
+  - kind: block
+    type: video
+    isVoid: true
+  - kind: block
+    type: video
+    isVoid: true