libcontainer/state_linux_test: Add a testTransitions helper

The helper DRYs up the transition tests and makes it easy to get
complete coverage for invalid transitions.

I'm also using t.Run() for subtests.  Run() is new in Go 1.7 [1], but
runc dropped support for 1.6 back in e773f96b (update go version at
travis-ci, 2017-02-20, #1335).

[1]: https://blog.golang.org/subtests

Signed-off-by: W. Trevor King <wking@tremily.us>

libcontainer/state_linux_test.go

@@ -2,16 +2,21 @@
 
 package libcontainer
 
-import "testing"
+import (
+	"reflect"
+	"testing"
+)
+
+var states = map[containerState]Status{
+	&createdState{}:          Created,
+	&runningState{}:          Running,
+	&restoredState{}:         Running,
+	&pausedState{}:           Paused,
+	&stoppedState{}:          Stopped,
+	&loadedState{s: Running}: Running,
+}
 
 func TestStateStatus(t *testing.T) {
-	states := map[containerState]Status{
-		&stoppedState{}:  Stopped,
-		&runningState{}:  Running,
-		&restoredState{}: Running,
-		&pausedState{}:   Paused,
-		&createdState{}:  Created,
-	}
 	for s, status := range states {
 		if s.status() != status {
 			t.Fatalf("state returned %s but expected %s", s.status(), status)
@@ -24,94 +29,88 @@ func isStateTransitionError(err error) bool {
 	return ok
 }
 
-func TestStoppedStateTransition(t *testing.T) {
-	s := &stoppedState{c: &linuxContainer{}}
-	valid := []containerState{
-		&stoppedState{},
-		&runningState{},
-		&restoredState{},
+func testTransitions(t *testing.T, initialState containerState, valid []containerState) {
+	validMap := map[reflect.Type]interface{}{}
+	for _, validState := range valid {
+		validMap[reflect.TypeOf(validState)] = nil
+		t.Run(validState.status().String(), func(t *testing.T) {
+			if err := initialState.transition(validState); err != nil {
+				t.Fatal(err)
+			}
+		})
 	}
-	for _, v := range valid {
-		if err := s.transition(v); err != nil {
-			t.Fatal(err)
+	for state := range states {
+		if _, ok := validMap[reflect.TypeOf(state)]; ok {
+			continue
 		}
+		t.Run(state.status().String(), func(t *testing.T) {
+			err := initialState.transition(state)
+			if err == nil {
+				t.Fatal("transition should fail")
+			}
+			if !isStateTransitionError(err) {
+				t.Fatal("expected stateTransitionError")
+			}
+		})
 	}
-	err := s.transition(&pausedState{})
-	if err == nil {
-		t.Fatal("transition to paused state should fail")
-	}
-	if !isStateTransitionError(err) {
-		t.Fatal("expected stateTransitionError")
-	}
+}
+
+func TestStoppedStateTransition(t *testing.T) {
+	testTransitions(
+		t,
+		&stoppedState{c: &linuxContainer{}},
+		[]containerState{
+			&stoppedState{},
+			&runningState{},
+			&restoredState{},
+		},
+	)
 }
 
 func TestPausedStateTransition(t *testing.T) {
-	s := &pausedState{c: &linuxContainer{}}
-	valid := []containerState{
-		&pausedState{},
-		&runningState{},
-		&stoppedState{},
-	}
-	for _, v := range valid {
-		if err := s.transition(v); err != nil {
-			t.Fatal(err)
-		}
-	}
+	testTransitions(
+		t,
+		&pausedState{c: &linuxContainer{}},
+		[]containerState{
+			&pausedState{},
+			&runningState{},
+			&stoppedState{},
+		},
+	)
 }
 
 func TestRestoredStateTransition(t *testing.T) {
-	s := &restoredState{c: &linuxContainer{}}
-	valid := []containerState{
-		&stoppedState{},
-		&runningState{},
-	}
-	for _, v := range valid {
-		if err := s.transition(v); err != nil {
-			t.Fatal(err)
-		}
-	}
-	err := s.transition(&createdState{})
-	if err == nil {
-		t.Fatal("transition to created state should fail")
-	}
-	if !isStateTransitionError(err) {
-		t.Fatal("expected stateTransitionError")
-	}
+	testTransitions(
+		t,
+		&restoredState{c: &linuxContainer{}},
+		[]containerState{
+			&stoppedState{},
+			&runningState{},
+		},
+	)
 }
 
 func TestRunningStateTransition(t *testing.T) {
-	s := &runningState{c: &linuxContainer{}}
-	valid := []containerState{
-		&stoppedState{},
-		&pausedState{},
-		&runningState{},
-	}
-	for _, v := range valid {
-		if err := s.transition(v); err != nil {
-			t.Fatal(err)
-		}
-	}
-
-	err := s.transition(&createdState{})
-	if err == nil {
-		t.Fatal("transition to created state should fail")
-	}
-	if !isStateTransitionError(err) {
-		t.Fatal("expected stateTransitionError")
-	}
+	testTransitions(
+		t,
+		&runningState{c: &linuxContainer{}},
+		[]containerState{
+			&stoppedState{},
+			&pausedState{},
+			&runningState{},
+		},
+	)
 }
 
 func TestCreatedStateTransition(t *testing.T) {
-	s := &createdState{c: &linuxContainer{}}
-	valid := []containerState{
-		&stoppedState{},
-		&pausedState{},
-		&runningState{},
-		&createdState{},
-	}
-	for _, v := range valid {
-		if err := s.transition(v); err != nil {
-			t.Fatal(err)
-		}
-	}
+	testTransitions(
+		t,
+		&createdState{c: &linuxContainer{}},
+		[]containerState{
+			&stoppedState{},
+			&pausedState{},
+			&runningState{},
+			&createdState{},
+		},
+	)
 }