add test coverage around ruleResult mutation

Author: Cache Hamm

test/engine-event.test.js

@@ -231,6 +231,26 @@ describe('Engine: event', () => {
 
   context('rule events: simple', () => {
     beforeEach(() => simpleSetup())
+
+    it('the rule result is a _copy_ of the rule`s conditions, and unaffected by mutation', async () => {
+      let rule = engine.rules[0]
+      let firstPass
+      rule.on('success', function (e, almanac, ruleResult) {
+        firstPass = ruleResult
+        delete ruleResult.conditions.any // subsequently modify the conditions in this rule result
+      })
+      await engine.run()
+
+      // run the engine again, now that ruleResult.conditions was modified
+      let secondPass
+      rule.on('success', function (e, almanac, ruleResult) {
+        secondPass = ruleResult
+      })
+      await engine.run()
+
+      expect(firstPass).to.deep.equal(secondPass) // second pass was unaffected by first pass
+    })
+
     it('on-success, it passes the event type and params', async () => {
       let failureSpy = sinon.spy()
       let successSpy = sinon.spy()