Step 9: refactor ensureDemonstration to "pop"

In general, when I can remove a logical branch from a delegator unit
(this unit is said to be a "delegator" because its primary task is 
offloading work onto other units), I'll usually rework the naming to 
push the branch down. Therefore, "ensureDemonstration" became 
"popDemonstration", and instead of simply providing a null-check and a
potential error, it will now pop the CallLog itself and blow up as 
necessary.

Does it really matter whose job that is? No, not really. But is the 
resulting `verify` module cleaner? Absolutely! It no longer mixes levels
of abstraction quite so much (notice how before it was a little odd how
the unit had awareness of a repository object as well as 5 business 
logic modules)

This refactor is a good example of the kind of thought process that
discovery testing encourages which I typically would never have 
undergone had I just written the code (or even "classical TDD'd" it)

src/verify/index.js

@@ -1,14 +1,11 @@
-import CallLog from '../value/call-log'
-
-import ensureDemonstration from './ensure-demonstration'
+import popDemonstration from './pop-demonstration'
 import didCallOccur from './did-call-occur'
 import notifySatisfiedMatchers from './notify-satisfied-matchers'
 import warnIfAlsoStubbed from './warn-if-also-stubbed'
 import fail from './fail'
 
 export default function verify (__userInvokesDemonstrationHere__, config) {
-  const {double, call} = CallLog.instance.pop() || {}
-  ensureDemonstration(call)
+  const {double, call} = popDemonstration()
   if (didCallOccur(double, call, config)) {
     notifySatisfiedMatchers(double, call, config)
     warnIfAlsoStubbed(double, call, config)

src/verify/pop-demonstration.js

@@ -0,0 +1,2 @@
+export default function popDemonstration () {
+}

test/unit/verify/index.test.js

@@ -1,12 +1,11 @@
 import Double from '../../../src/value/double'
 import Call from '../../../src/value/call'
-import CallLog from '../../../src/value/call-log'
 
-let subject, ensureDemonstration, didCallOccur, notifySatisfiedMatchers,
+let subject, popDemonstration, didCallOccur, notifySatisfiedMatchers,
     warnIfAlsoStubbed, fail
 module.exports = {
   beforeEach: () => {
-    ensureDemonstration = td.replace('../../../src/verify/ensure-demonstration').default
+    popDemonstration = td.replace('../../../src/verify/pop-demonstration').default
     didCallOccur = td.replace('../../../src/verify/did-call-occur').default
     notifySatisfiedMatchers = td.replace('../../../src/verify/notify-satisfied-matchers').default
     warnIfAlsoStubbed = td.replace('../../../src/verify/warn-if-also-stubbed').default
@@ -16,34 +15,32 @@ module.exports = {
   'verified to have occurred as configured': () => {
     const double = new Double()
     const call = new Call()
-    CallLog.instance.log(double, call)
     const config = {some: 'option'}
+    td.when(popDemonstration()).thenReturn({double, call})
     td.when(didCallOccur(double, call, config)).thenReturn(true)
 
     subject(/*imagine double('a','b','c')*/ undefined, config)
 
-    td.verify(ensureDemonstration(call))
     td.verify(notifySatisfiedMatchers(double, call, config))
     td.verify(warnIfAlsoStubbed(double, call, config))
     assert.equal(td.explain(fail).callCount, 0)
   },
   'demonstrated call DID NOT occur, failing test': () => {
     const double = new Double()
     const call = new Call()
-    CallLog.instance.log(double, call)
     const config = {some: 'option'}
+    td.when(popDemonstration()).thenReturn({double, call})
     td.when(didCallOccur(double, call, config)).thenReturn(false)
 
     subject(/*imagine double('a','b','X')*/ undefined, config)
 
-    td.verify(ensureDemonstration(call))
     td.verify(fail(double, call, config))
     assert.equal(td.explain(notifySatisfiedMatchers).callCount, 0)
     assert.equal(td.explain(warnIfAlsoStubbed).callCount, 0)
   },
   'demonstration missing blows up': () => {
     const config = {some: 'option'}
-    td.when(ensureDemonstration(undefined)).thenThrow(new Error('wups'))
+    td.when(popDemonstration()).thenThrow(new Error('wups'))
 
     assert.throws(() => {
       subject(/*imagine double('a','b','X')*/ undefined, config)