Reset the strategy registry on each run

These conditions ...

 - the pipeline reconciler is constructed in TestMain;
 - the test setup appends the mock strategy to the reconciler's
   strategies;
 - the mock strategy operates on values in its closure;
 - the first strategy answering `true` to Handle(...) will be used;

... all together mean that when you run the test case more than
once, it will end up running the mock strategy on apps that aren't
used any more.

We decided earlier that replacing the whole set of strategies broke
encapsulation too much; but, I think it may be the simplest way to
make the test repeatable.

These are alternatives I considered:

 - construct the reconciler anew for each test case (drags in the
   manager, then other things ...);

 - have a `Reset` method for the strategies (I don't like exporting
   methods just for testing);

 - refer to the app values indirectly, e.g., by having the mock
   strategy refer to a func which is re-assigned, rather than inlining
   it (would have to ensure the mock is installed once, but the func
   is reassigned -- awkward)

Signed-off-by: Michael Bridgen <[email protected]>

controllers/leveltriggered/promote_test.go

@@ -37,7 +37,7 @@ func TestPromotionAlgorithm(t *testing.T) {
 	prodApp := createApp(ctx, k8sClient, g, appName, prodNs.Name)
 	setAppRevisionAndReadyStatus(ctx, g, prodApp, "v1.0.0")
 
-	mockStrategy := setStrategyRegistry(t, pipelineReconciler)
+	mockStrategy := installMockStrategy(t, pipelineReconciler)
 	mockStrategy.EXPECT().Handles(gomock.Any()).Return(true).AnyTimes()
 
 	mockStrategy.EXPECT().
@@ -226,7 +226,8 @@ func setAppStatusReadyCondition(ctx context.Context, g Gomega, hr *helmv2.HelmRe
 	g.Expect(k8sClient.Status().Update(ctx, hr)).To(Succeed())
 }
 
-func setStrategyRegistry(t *testing.T, r *PipelineReconciler) *strategy.MockStrategy {
+func installMockStrategy(t *testing.T, r *PipelineReconciler) *strategy.MockStrategy {
+	r.stratReg = strategy.StrategyRegistry{}
 	mockCtrl := gomock.NewController(t)
 	mockStrategy := strategy.NewMockStrategy(mockCtrl)