fix: update props when watcher depends on value (#842)

Author: eddyerburgh

Diff for: packages/test-utils/src/wrapper.js

@@ -674,12 +674,17 @@ export default class Wrapper implements BaseWrapper {
       }
 
       if (this.vm && this.vm._props) {
+        // Set actual props value
         this.vm._props[key] = data[key]
-      } else {
         // $FlowIgnore : Problem with possibly null this.vm
         this.vm[key] = data[key]
+      } else {
         // $FlowIgnore : Problem with possibly null this.vm.$options
         this.vm.$options.propsData[key] = data[key]
+        // $FlowIgnore : Problem with possibly null this.vm
+        this.vm[key] = data[key]
+        // $FlowIgnore : Need to call this twice to fix watcher bug in 2.0.x
+        this.vm[key] = data[key]
       }
     })
     // $FlowIgnore : Problem with possibly null this.vm

Diff for: test/specs/wrapper/setProps.spec.js

@@ -199,6 +199,24 @@ describeWithShallowAndMount('setProps', mountingMethod => {
       .with.property('message', message)
   })
 
+  it('updates watched prop', () => {
+    const TestComponent = {
+      template: '<div />',
+      props: ['propA'],
+      mounted () {
+        this.$watch('propA', function () {
+          this.propA
+        }, { immediate: true }
+        )
+      }
+    }
+    const wrapper = mountingMethod(TestComponent, { propsData: { propA: 'none' }})
+
+    wrapper.setProps({ propA: 'value' })
+    expect(wrapper.props().propA).to.equal('value')
+    expect(wrapper.vm.propA).to.equal('value')
+  })
+
   it('throws an error if node is not a Vue instance', () => {
     const message = 'wrapper.setProps() can only be called on a Vue instance'
     const compiled = compileToFunctions('<div><p></p></div>')