diff --git a/container/msg.go b/container/msg.go
index 4be0fd2..1512a58 100644
--- a/container/msg.go
+++ b/container/msg.go
@@ -50,3 +50,18 @@ func (msg *DefaultMsg) Verbosef(format string, v ...any) {
 func (msg *DefaultMsg) Suspend()     { msg.inactive.Store(true) }
 func (msg *DefaultMsg) Resume() bool { return msg.inactive.CompareAndSwap(true, false) }
 func (msg *DefaultMsg) BeforeExit()  {}
+
+// msg is the [Msg] implemented used by all exported [container] functions.
+var msg Msg = new(DefaultMsg)
+
+// GetOutput returns the current active [Msg] implementation.
+func GetOutput() Msg { return msg }
+
+// SetOutput replaces the current active [Msg] implementation.
+func SetOutput(v Msg) {
+	if v == nil {
+		msg = new(DefaultMsg)
+	} else {
+		msg = v
+	}
+}
diff --git a/container/msg_test.go b/container/msg_test.go
index ba62e9d..1b36a1d 100644
--- a/container/msg_test.go
+++ b/container/msg_test.go
@@ -146,3 +146,39 @@ func (out *testOutput) Resume() bool {
 }
 
 func (out *testOutput) BeforeExit() { out.Verbose("beforeExit called") }
+
+func TestGetSetOutput(t *testing.T) {
+	{
+		out := container.GetOutput()
+		t.Cleanup(func() { container.SetOutput(out) })
+	}
+
+	t.Run("default", func(t *testing.T) {
+		container.SetOutput(new(stubOutput))
+		if v, ok := container.GetOutput().(*container.DefaultMsg); ok {
+			t.Fatalf("SetOutput: got unexpected output %#v", v)
+		}
+		container.SetOutput(nil)
+		if _, ok := container.GetOutput().(*container.DefaultMsg); !ok {
+			t.Fatalf("SetOutput: got unexpected output %#v", container.GetOutput())
+		}
+	})
+
+	t.Run("stub", func(t *testing.T) {
+		container.SetOutput(new(stubOutput))
+		if _, ok := container.GetOutput().(*stubOutput); !ok {
+			t.Fatalf("SetOutput: got unexpected output %#v", container.GetOutput())
+		}
+	})
+}
+
+type stubOutput struct {
+	wrapF func(error, ...any) error
+}
+
+func (*stubOutput) IsVerbose() bool         { panic("unreachable") }
+func (*stubOutput) Verbose(...any)          { panic("unreachable") }
+func (*stubOutput) Verbosef(string, ...any) { panic("unreachable") }
+func (*stubOutput) Suspend()                { panic("unreachable") }
+func (*stubOutput) Resume() bool            { panic("unreachable") }
+func (*stubOutput) BeforeExit()             { panic("unreachable") }
diff --git a/container/output.go b/container/output.go
index 86f57c8..4d799eb 100644
--- a/container/output.go
+++ b/container/output.go
@@ -75,14 +75,3 @@ func (s *Suspendable) Resume() (resumed bool, dropped uintptr, n int64, err erro
 	}
 	return
 }
-
-var msg Msg = new(DefaultMsg)
-
-func GetOutput() Msg { return msg }
-func SetOutput(v Msg) {
-	if v == nil {
-		msg = new(DefaultMsg)
-	} else {
-		msg = v
-	}
-}
diff --git a/container/output_test.go b/container/output_test.go
index 54eba8f..cfa8e0d 100644
--- a/container/output_test.go
+++ b/container/output_test.go
@@ -1,4 +1,4 @@
-package container
+package container_test
 
 import (
 	"bytes"
@@ -8,10 +8,14 @@ import (
 	"syscall"
 	"testing"
 
+	"hakurei.app/container"
 	"hakurei.app/container/stub"
 )
 
 func TestSuspendable(t *testing.T) {
+	// copied from output.go
+	const suspendBufMax = 1 << 24
+
 	const (
 		// equivalent to len(want.pt)
 		nSpecialPtEquiv = -iota - 1
@@ -70,7 +74,7 @@ func TestSuspendable(t *testing.T) {
 
 	var dw expectWriter
 
-	w := Suspendable{Downstream: &dw}
+	w := container.Suspendable{Downstream: &dw}
 	for _, tc := range testCases {
 		// these share the same writer, so cannot be subtests
 		t.Logf("writing step %q", tc.name)
@@ -149,39 +153,3 @@ func (w *expectWriter) Write(p []byte) (n int, err error) {
 	}
 	return
 }
-
-func TestGetSetOutput(t *testing.T) {
-	{
-		out := GetOutput()
-		t.Cleanup(func() { SetOutput(out) })
-	}
-
-	t.Run("default", func(t *testing.T) {
-		SetOutput(new(stubOutput))
-		if v, ok := GetOutput().(*DefaultMsg); ok {
-			t.Fatalf("SetOutput: got unexpected output %#v", v)
-		}
-		SetOutput(nil)
-		if _, ok := GetOutput().(*DefaultMsg); !ok {
-			t.Fatalf("SetOutput: got unexpected output %#v", GetOutput())
-		}
-	})
-
-	t.Run("stub", func(t *testing.T) {
-		SetOutput(new(stubOutput))
-		if _, ok := GetOutput().(*stubOutput); !ok {
-			t.Fatalf("SetOutput: got unexpected output %#v", GetOutput())
-		}
-	})
-}
-
-type stubOutput struct {
-	wrapF func(error, ...any) error
-}
-
-func (*stubOutput) IsVerbose() bool         { panic("unreachable") }
-func (*stubOutput) Verbose(...any)          { panic("unreachable") }
-func (*stubOutput) Verbosef(string, ...any) { panic("unreachable") }
-func (*stubOutput) Suspend()                { panic("unreachable") }
-func (*stubOutput) Resume() bool            { panic("unreachable") }
-func (*stubOutput) BeforeExit()             { panic("unreachable") }