diff --git a/parse.go b/parse.go
index 169e8cc..45e4751 100644
--- a/parse.go
+++ b/parse.go
@@ -86,13 +86,6 @@ func MustParse(dest ...interface{}) *Parser {
 
 // mustParse is a helper that facilitates testing
 func mustParse(config Config, dest ...interface{}) *Parser {
-	if config.Exit == nil {
-		config.Exit = os.Exit
-	}
-	if config.Out == nil {
-		config.Out = os.Stdout
-	}
-
 	p, err := NewParser(config, dest...)
 	if err != nil {
 		fmt.Fprintln(config.Out, err)
diff --git a/parse_test.go b/parse_test.go
index d53b483..fe055fe 100644
--- a/parse_test.go
+++ b/parse_test.go
@@ -1737,3 +1737,11 @@ func TestSubcommandGlobalFlag_InCommand_Strict_Inner(t *testing.T) {
 	require.NotNil(t, args.Sub)
 	assert.True(t, args.Sub.Guard)
 }
+
+func TestExitFunctionAndOutStreamGetFilledIn(t *testing.T) {
+	var args struct{}
+	p, err := NewParser(Config{}, &args)
+	require.NoError(t, err)
+	assert.NotNil(t, p.config.Exit) // go prohibits function pointer comparison
+	assert.Equal(t, p.config.Out, os.Stdout)
+}
diff --git a/usage_test.go b/usage_test.go
index b1693a9..612d573 100644
--- a/usage_test.go
+++ b/usage_test.go
@@ -260,6 +260,39 @@ Options:
 	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
 }
 
+type userDefinedVersionFlag struct {
+	ShowVersion bool `arg:"--version" help:"this is a user-defined version flag"`
+}
+
+// Version returns the version for this program
+func (userDefinedVersionFlag) Version() string {
+	return "example 3.2.1"
+}
+
+func TestUsageWithUserDefinedVersionFlag(t *testing.T) {
+	expectedUsage := "example 3.2.1\nUsage: example [--version]"
+
+	expectedHelp := `
+example 3.2.1
+Usage: example [--version]
+
+Options:
+  --version              this is a user-defined version flag
+  --help, -h             display this help and exit
+`
+	os.Args[0] = "example"
+	p, err := NewParser(Config{}, &userDefinedVersionFlag{})
+	require.NoError(t, err)
+
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
+}
+
 type described struct{}
 
 // Described returns the description for this program
@@ -415,6 +448,50 @@ Options:
 	assert.Equal(t, expectedUsage, usage.String())
 }
 
+func TestUsageWithSubcommands(t *testing.T) {
+	expectedUsage := "Usage: example child [--values VALUES]"
+
+	expectedHelp := `
+Usage: example child [--values VALUES]
+
+Options:
+  --values VALUES        Values
+
+Global options:
+  --verbose, -v          verbosity level
+  --help, -h             display this help and exit
+`
+
+	var args struct {
+		Verbose bool `arg:"-v" help:"verbosity level"`
+		Child   *struct {
+			Values []float64 `help:"Values"`
+		} `arg:"subcommand:child"`
+	}
+
+	os.Args[0] = "example"
+	p, err := NewParser(Config{}, &args)
+	require.NoError(t, err)
+
+	_ = p.Parse([]string{"child"})
+
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var help2 bytes.Buffer
+	p.WriteHelpForSubcommand(&help2, "child")
+	assert.Equal(t, expectedHelp[1:], help2.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
+
+	var usage2 bytes.Buffer
+	p.WriteUsageForSubcommand(&usage2, "child")
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage2.String()))
+}
+
 func TestUsageWithNestedSubcommands(t *testing.T) {
 	expectedUsage := "Usage: example child nested [--enable] OUTPUT"