Take back the test store's lock fix: open #148 carries the fuller one

Merged beside #148 the two would not compile (SetFail declared twice, m.Fail undefined). #148 lands on its own.

internal/conditions/memory.go

@@ -61,14 +61,6 @@ func (m *InMemory) Update(_ context.Context, key string, value []byte, revision
 	return nil
 }
 
-// SetFail makes every call fail with err from now on, or none with nil: under the store's lock, so a test may
-// change it while the keeper's own goroutine is telling.
-func (m *InMemory) SetFail(err error) {
-	m.mu.Lock()
-	defer m.mu.Unlock()
-	m.Fail = err
-}
-
 func (m *InMemory) Delete(_ context.Context, key string, revision uint64) error {
 	m.mu.Lock()
 	defer m.mu.Unlock()

internal/conditions/store_test.go

@@ -199,17 +199,15 @@ func TestAnUnreadableStoreClearsNothing(t *testing.T) {
 	if _, err := k.Observe(ctx, silent("ace")); err != nil {
 		t.Fatal(err)
 	}
-	store.SetFail(errors.New("the bus is away"))
+	store.Fail = errors.New("the bus is away")
 	if err := k.Reconcile(ctx, "S1", nil); err == nil {
 		t.Fatal("reconciled against a store it could not read")
 	}
 	if _, err := k.Open(ctx); err == nil {
 		t.Fatal("an unreadable store answered as read")
 	}
-	store.SetFail(nil)
-	store.mu.Lock()
+	store.Fail = nil
 	store.values["machine.g14.silent"] = Entry{Value: []byte("{not a condition"), Revision: 99}
-	store.mu.Unlock()
 	if _, err := k.Open(ctx); err == nil || !strings.Contains(err.Error(), "machine.g14.silent") {
 		t.Fatalf("an unreadable condition was left out rather than said: %v", err)
 	}