Fix flaky TestServiceLogs due to TestCurrentUserGroup reusing manager (…

…#242)

This was causing intermittent failures in TestServiceLogs (on the order
of 50% of the time), see test failure output below.

START: manager_test.go:456: S.TestServiceLogs
START: manager_test.go:147: S.SetUpTest
PASS: manager_test.go:147: S.SetUpTest	0.000s

2023-06-19T11:13:02.294Z [test] Service "test1" starting: /bin/sh -c "echo test1 | tee -a /tmp/check-270658404/27/log.txt; sleep 10"
2023-06-19T11:13:02.346Z [test] Service "test2" starting: /bin/sh -c "echo test2 | tee -a /tmp/check-270658404/27/log.txt; sleep 10"
2023-06-19T11:13:02.368Z [test] Service "usrtest" starting: /bin/sh -c "id -n -u | tee -a /tmp/check-270658404/8/log.txt; sleep 0.060000000000000005"
manager_test.go:461:
    s.testServiceLogs(c, outputs)
manager_test.go:204:
    c.Assert(s.logBuffer.String(), Matches, "(?s)"+expected)
... value string = "" +
...     "2023-06-19T11:13:02.300Z [test1] test1\n" +
...     "2023-06-19T11:13:02.348Z [test2] test2\n" +
...     "2023-06-19T11:13:02.372Z [usrtest] runner\n"
... regex string = "" +
...     "(?s).*test1\n" +
...     ".*test2\n"

START: manager_test.go:183: S.TearDownTest
PASS: manager_test.go:183: S.TearDownTest	0.000s

FAIL: manager_test.go:456: S.TestServiceLogs

internals/overlord/servstate/manager_test.go

@@ -506,33 +506,40 @@ func (s *S) TestStartBadCommand(c *C) {
 }
 
 func (s *S) TestCurrentUserGroup(c *C) {
+	// Don't re-use s.manager, because we're adding a layer and service, and
+	// that would conflict with other tests like TestServiceLogs.
+	dir := c.MkDir()
+	err := os.Mkdir(filepath.Join(dir, "layers"), 0755)
+	c.Assert(err, IsNil)
+	manager, err := servstate.NewManager(s.st, s.runner, dir, nil, nil, fakeLogManager{})
+	c.Assert(err, IsNil)
+	defer manager.Stop()
+
 	current, err := user.Current()
 	c.Assert(err, IsNil)
 	group, err := user.LookupGroupId(current.Gid)
 	c.Assert(err, IsNil)
 
-	layer := parseLayer(c, 0, "layer99", fmt.Sprintf(`
+	outputPath := filepath.Join(dir, "output")
+	layer := parseLayer(c, 0, "layer", fmt.Sprintf(`
 services:
     usrtest:
         override: replace
-        command: /bin/sh -c "id -n -u | tee -a %s; sleep %g"
+        command: /bin/sh -c "id -n -u >%s; sleep %g"
         user: %s
         group: %s
-`, s.log, shortOkayDelay.Seconds()+0.01, current.Username, group.Name))
-	err = s.manager.AppendLayer(layer)
-	c.Assert(err, IsNil)
-	_, _, err = s.manager.Replan()
+`, outputPath, shortOkayDelay.Seconds()+0.01, current.Username, group.Name))
+	err = manager.AppendLayer(layer)
 	c.Assert(err, IsNil)
 
 	chg := s.startServices(c, []string{"usrtest"}, 1)
 	s.st.Lock()
 	c.Assert(chg.Err(), IsNil)
 	s.st.Unlock()
 
-	s.waitUntilService(c, "usrtest", func(service *servstate.ServiceInfo) bool {
-		return service.Current == servstate.StatusBackoff
-	})
-	s.assertLog(c, ".*"+current.Username+"\n")
+	output, err := ioutil.ReadFile(outputPath)
+	c.Assert(err, IsNil)
+	c.Check(string(output), Equals, current.Username+"\n")
 }
 
 func (s *S) TestUserGroupFails(c *C) {