func (s *upgradeSuite) TestPerformUpgrade(c *gc.C) {
	s.PatchValue(upgrades.UpgradeOperations, upgradeOperations)
	for i, test := range upgradeTests {
		c.Logf("%d: %s", i, test.about)
		var messages []string
		ctx := &mockContext{
			messages: messages,
		}
		fromVersion := version.Zero
		if test.fromVersion != "" {
			fromVersion = version.MustParse(test.fromVersion)
		}
		toVersion := version.MustParse("1.18.0")
		if test.toVersion != "" {
			toVersion = version.MustParse(test.toVersion)
		}
		vers := version.Current
		vers.Number = toVersion
		s.PatchValue(&version.Current, vers)
		err := upgrades.PerformUpgrade(fromVersion, test.target, ctx)
		if test.err == "" {
			c.Check(err, gc.IsNil)
		} else {
			c.Check(err, gc.ErrorMatches, test.err)
		}
		c.Check(ctx.messages, jc.DeepEquals, test.expectedSteps)
	}
}

func (s *upgradeSuite) TestStateStepsNotAttemptedWhenNoStateTarget(c *gc.C) {
	stateCount := 0
	stateUpgradeOperations := func() []upgrades.Operation {
		stateCount++
		return nil
	}
	s.PatchValue(upgrades.StateUpgradeOperations, stateUpgradeOperations)

	apiCount := 0
	upgradeOperations := func() []upgrades.Operation {
		apiCount++
		return nil
	}
	s.PatchValue(upgrades.UpgradeOperations, upgradeOperations)

	fromVers := version.MustParse("1.18.0")
	ctx := new(mockContext)
	check := func(target upgrades.Target, expectedStateCallCount int) {
		stateCount = 0
		apiCount = 0
		err := upgrades.PerformUpgrade(fromVers, targets(target), ctx)
		c.Assert(err, jc.ErrorIsNil)
		c.Assert(stateCount, gc.Equals, expectedStateCallCount)
		c.Assert(apiCount, gc.Equals, 1)
	}

	check(upgrades.Controller, 1)
	check(upgrades.DatabaseMaster, 1)
	check(upgrades.AllMachines, 0)
	check(upgrades.HostMachine, 0)
}

// runUpgrades runs the upgrade operations for each job type and updates the updatedToVersion on success.
func (a *MachineAgent) runUpgrades(
	st *state.State,
	apiState *api.State,
	jobs []params.MachineJob,
	agentConfig agent.Config,
) error {
	from := version.Current
	from.Number = agentConfig.UpgradedToVersion()
	if from == version.Current {
		logger.Infof("upgrade to %v already completed.", version.Current)
		return nil
	}
	var err error
	writeErr := a.ChangeConfig(func(agentConfig agent.ConfigSetter) {
		context := upgrades.NewContext(agentConfig, apiState, st)
		for _, job := range jobs {
			target := upgradeTarget(job)
			if target == "" {
				continue
			}
			logger.Infof("starting upgrade from %v to %v for %v %q", from, version.Current, target, a.Tag())
			if err = upgrades.PerformUpgrade(from.Number, target, context); err != nil {
				err = fmt.Errorf("cannot perform upgrade from %v to %v for %v %q: %v", from, version.Current, target, a.Tag(), err)
				return
			}
		}
		agentConfig.SetUpgradedToVersion(version.Current.Number)
	})
	if writeErr != nil {
		return fmt.Errorf("cannot write updated agent configuration: %v", writeErr)
	}
	return nil
}

func (s *upgradeSuite) checkContextRestriction(c *gc.C, expectedPanic string) {
	fromVersion := version.MustParse("1.20.0")
	type fakeAgentConfigSetter struct{ agent.ConfigSetter }
	ctx := upgrades.NewContext(fakeAgentConfigSetter{}, nil, new(state.State))
	c.Assert(
		func() { upgrades.PerformUpgrade(fromVersion, targets(upgrades.Controller), ctx) },
		gc.PanicMatches, expectedPanic,
	)
}