controller/vm: add unit tests for VM Controller state machine

Add 42 test cases for the VM Controller covering state transitions,
guard checks, idempotency, and method behavior. Change Manager.uvm
and Manager.guest to interface types to enable mock injection.

Tests: TerminateVM transitions, ExecIntoHost, DumpStacks, StartTime,
ExitStatus, StartVM idempotency, State.String(), and guard checks for
all state-dependent methods.

Generated mocks for LifetimeManager, GuestManager, and
GuestDefinedCapabilities using mockgen.

Signed-off-by: Shreyansh Sancheti <shreyanshjain7174@gmail.com>
Signed-off-by: Shreyansh Sancheti <shsancheti@microsoft.com>

Author: Shreyansh Sancheti

internal/controller/vm/export_test.go

@@ -0,0 +1,17 @@
+//go:build windows
+
+package vm
+
+import (
+	"github.com/Microsoft/hcsshim/internal/vm/vmmanager"
+)
+
+// SetManagerForTest configures a Manager with injected dependencies for testing.
+// This is only available in test builds.
+//
+// MUST be called during test setup before any concurrent operations on the Manager.
+func (c *Manager) SetManagerForTest(uvm vmmanager.LifetimeManager, guest GuestManager, state State) {
+	c.uvm = uvm
+	c.guest = guest
+	c.vmState = state
+}

internal/controller/vm/interface.go

@@ -2,6 +2,8 @@
 
 package vm
 
+//go:generate go tool mockgen -source=interface.go -build_constraint=windows -package=mockvmcontroller -destination=../../test/mock/vmcontroller/mock_interface.go
+
 import (
 	"context"
 	"time"
@@ -15,9 +17,18 @@ import (
 	"github.com/Microsoft/go-winio/pkg/guid"
 )
 
+// GuestManager defines the guest operations required by the VM Controller.
+// It combines the core guest manager, security policy, and HvSocket interfaces
+// from the guestmanager package into a single interface for dependency injection.
+type GuestManager interface {
+	guestmanager.Manager
+	guestmanager.SecurityPolicyManager
+	guestmanager.HVSocketManager
+}
+
 type Controller interface {
 	// Guest returns the guest manager instance for this VM.
-	Guest() *guestmanager.Guest
+	Guest() GuestManager
 
 	// State returns the current VM state.
 	State() State

internal/controller/vm/state_test.go

@@ -0,0 +1,33 @@
+//go:build windows
+
+package vm_test
+
+import (
+	"testing"
+
+	vm "github.com/Microsoft/hcsshim/internal/controller/vm"
+)
+
+func TestStateString(t *testing.T) {
+	tests := []struct {
+		state vm.State
+		want  string
+	}{
+		{vm.StateNotCreated, "NotCreated"},
+		{vm.StateCreated, "Created"},
+		{vm.StateRunning, "Running"},
+		{vm.StateTerminated, "Terminated"},
+		{vm.StateInvalid, "Invalid"},
+		{vm.State(99), "Unknown"},
+		{vm.State(-1), "Unknown"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.want, func(t *testing.T) {
+			t.Parallel()
+			if got := tt.state.String(); got != tt.want {
+				t.Errorf("State(%d).String() = %q, want %q", tt.state, got, tt.want)
+			}
+		})
+	}
+}

internal/controller/vm/vm.go

@@ -33,8 +33,8 @@ import (
 // and its associated resources.
 type Manager struct {
 	vmID  string
-	uvm   *vmmanager.UtilityVM
-	guest *guestmanager.Guest
+	uvm   vmmanager.LifetimeManager
+	guest GuestManager
 
 	// vmState tracks the current state of the VM lifecycle.
 	// Access must be guarded by mu.
@@ -70,7 +70,7 @@ func NewController() *Manager {
 
 // Guest returns the guest manager instance for this VM.
 // The guest manager provides access to guest-host communication.
-func (c *Manager) Guest() *guestmanager.Guest {
+func (c *Manager) Guest() GuestManager {
 	return c.guest
 }