add failing driver and server tests for circular objs over websocket

packages/driver/test/cypress/integration/cypress/cypress_spec.coffee

@@ -47,6 +47,18 @@ describe "driver/src/cypress/index", ->
 
         done()
 
+    ## https://github.com/cypress-io/cypress/issues/4346
+    it "can complete if a circular reference is sent", ->
+      foo = {
+        bar: {}
+      }
+
+      foo.bar.baz = foo
+
+      Cypress.backend("foo", foo)
+      .catch (e) ->
+        expect(e.message).to.eq('You requested a backend event we cannot handle: foo')
+
   context ".isCy", ->
     it "returns true on cy, cy chainable", ->
       expect(Cypress.isCy(cy)).to.be.true
@@ -75,4 +87,4 @@ describe "driver/src/cypress/index", ->
       fn = ->
         Cypress.log({ message: 'My Log' })
 
-      expect(fn).to.not.throw()
+      expect(fn).to.not.throw()

packages/server/test/unit/socket_spec.coffee

@@ -70,6 +70,22 @@ describe "lib/socket", ->
     afterEach ->
       @client.disconnect()
 
+    ## https://github.com/cypress-io/cypress/issues/4346
+    it "can emit a circular object without crashing", (done) ->
+      foo = {
+        bar: {}
+      }
+
+      foo.bar.baz = foo
+
+      ## going to stub exec here just so we have something that we can
+      ## control the resolved value of
+      sinon.stub(exec, 'run').resolves(foo)
+
+      @client.emit "backend:request", "exec", "quuz", (res) ->
+        expect(res).to.deep.eq(foo)
+        done()
+
     context "on(automation:request)", ->
       describe "#onAutomation", ->
         before ->