Set deepest nested service to current

This makes it so that we always use the deepest nested service as the `current`.

This is not a breaking change as this is current expected behavior. We were passing `service.child` to be the new current, but not accounting for the possibility of deeply nested machines.

Fixes #195

packages/core/machine.js

@@ -169,8 +169,9 @@ function transitionTo(service, machine, fromEvent, candidates) {
       if (d._onEnter) d._onEnter(machine, to, service.context, context, fromEvent);
       let state = newMachine.state.value;
       service.machine = newMachine;
+      let ret = state.enter(newMachine, service, fromEvent);
       service.onChange(service);
-      return state.enter(newMachine, service, fromEvent);
+      return ret;
     }
   }
 }

packages/robot-hooks/machine.js

@@ -24,7 +24,11 @@ export function createUseMachine(useEffect, useState) {
         if (!mounted) {
           return;
         }
-        setCurrent(createCurrent(service.child || service));
+        let currentService = service;
+        while(currentService.child) {
+          currentService = currentService.child;
+        }
+        setCurrent(createCurrent(currentService));
       }, data || initialContext);
     }
 

packages/robot-hooks/test/test.js

@@ -133,12 +133,19 @@ QUnit.module('useMachine', hooks => {
     el.remove();
   });
 
-  QUnit.skip('Invoking machines the "current" is the child machine', async assert => {
+  QUnit.test('Invoking machines the "current" is the child machine', async assert => {
+    const deep = createMachine({
+      deepOne: state(
+        transition('next', 'deepTwo')
+      ),
+      deepTwo: state(),
+    })
     const nested = createMachine({
       nestedOne: state(
         transition('next', 'nestedTwo')
       ),
-      nestedTwo: state()
+      nestedTwo: invoke(deep, transition('done', 'nestedThree')),
+      nestedThree: state()
     });
     const machine = createMachine({
       one: state(
@@ -150,11 +157,9 @@ QUnit.module('useMachine', hooks => {
       three: state()
     });
 
-    let current, send, service;
+    let service;
     function App() {
-      const [currentState, sendEvent, thisService] = useMachine(machine);
-      current = currentState;
-      send = sendEvent;
+      const [current, _send, thisService] = useMachine(machine);
       service = thisService;
 
       return html`
@@ -167,10 +172,13 @@ QUnit.module('useMachine', hooks => {
       let text = () => el.textContent.trim();
 
       assert.equal(text(), 'State: one');
-      yield send('next');
+      yield service.send('next');
 
       assert.equal(text(), 'State: nestedOne');
       yield service.child.send('next');
+
+      assert.equal(text(), 'State: deepOne');
+      yield service.child.child.send('next');
 
       assert.equal(text(), 'State: three');
     });