Merge pull request juju#16115 from manadart/3.1-action-pruner-test-fix

juju#16115

JUJU-4435

`TestRunStop` from the action-pruner worker suite starts a watcher at the top of its event loop. The test kills the worker immediately, but the first selected case will sometimes be the initial event for the watcher instead of the killed catacomb.

Here we accommodate this possibility and mock the `ModelConfig` method.

## QA steps

Worker tests for `actionpruner` pass consistently.

worker/actionpruner/worker_test.go

@@ -14,6 +14,8 @@ import (
 	gc "gopkg.in/check.v1"
 
 	"github.com/juju/juju/core/watcher/watchertest"
+	"github.com/juju/juju/environs/config"
+	coretesting "github.com/juju/juju/testing"
 	"github.com/juju/juju/worker/actionpruner"
 	"github.com/juju/juju/worker/pruner"
 	"github.com/juju/juju/worker/pruner/mocks"
@@ -27,18 +29,33 @@ func (s *PrunerSuite) TestRunStop(c *gc.C) {
 	ctrl := gomock.NewController(c)
 	defer ctrl.Finish()
 
+	cfg, err := config.New(false, map[string]interface{}{
+		"name":                    "test",
+		"type":                    "manual",
+		"uuid":                    coretesting.ModelTag.Id(),
+		"max-action-results-age":  "2h",
+		"max-action-results-size": "2GiB",
+	})
+	c.Assert(err, jc.ErrorIsNil)
+
 	ch := make(chan struct{}, 1)
 	ch <- struct{}{}
 	w := watchertest.NewMockNotifyWatcher(ch)
 
 	facade := mocks.NewMockFacade(ctrl)
 	facade.EXPECT().WatchForModelConfigChanges().Return(w, nil)
+
+	// Depending on the host compute speed, the loop may select either
+	// the watcher change event, or the catacomb's dying event first.
+	facade.EXPECT().ModelConfig().Return(cfg, nil).AnyTimes()
+
 	updater, err := actionpruner.New(pruner.Config{
 		Facade:        facade,
-		PruneInterval: 0,
+		PruneInterval: time.Minute,
 		Clock:         testclock.NewClock(time.Now()),
 		Logger:        loggo.GetLogger("test"),
 	})
+
 	c.Assert(err, jc.ErrorIsNil)
 	workertest.CleanKill(c, updater)
 }