Merge pull request #150 from alexflint/push-coverage-up-more

Push test coverage up to 100%

example_test.go

@@ -95,6 +95,19 @@ func Example_mappings() {
 	// output: map[john:123 mary:456]
 }
 
+// This example demonstrates arguments with keys and values separated by commas
+func Example_mappingsWithCommas() {
+	// The args you would pass in on the command line
+	os.Args = split("./example --userids john=123 mary=456")
+
+	var args struct {
+		UserIDs map[string]int
+	}
+	MustParse(&args)
+	fmt.Println(args.UserIDs)
+	// output: map[john:123 mary:456]
+}
+
 // This eample demonstrates multiple value arguments that can be mixed with
 // other arguments.
 func Example_multipleMixed() {
@@ -130,6 +143,7 @@ func Example_helpText() {
 
 	// This is only necessary when running inside golang's runnable example harness
 	osExit = func(int) {}
+	stdout = os.Stdout
 
 	MustParse(&args)
 
@@ -162,6 +176,7 @@ func Example_helpPlaceholder() {
 
 	// This is only necessary when running inside golang's runnable example harness
 	osExit = func(int) {}
+	stdout = os.Stdout
 
 	MustParse(&args)
 
@@ -202,6 +217,7 @@ func Example_helpTextWithSubcommand() {
 
 	// This is only necessary when running inside golang's runnable example harness
 	osExit = func(int) {}
+	stdout = os.Stdout
 
 	MustParse(&args)
 
@@ -239,6 +255,7 @@ func Example_helpTextForSubcommand() {
 
 	// This is only necessary when running inside golang's runnable example harness
 	osExit = func(int) {}
+	stdout = os.Stdout
 
 	MustParse(&args)
 

parse.go

@@ -13,9 +13,6 @@ import (
 	scalar "github.com/alexflint/go-scalar"
 )
 
-// to enable monkey-patching during tests
-var osExit = os.Exit
-
 // path represents a sequence of steps to find the output location for an
 // argument or subcommand in the final destination struct
 type path struct {
@@ -80,7 +77,7 @@ var ErrVersion = errors.New("version requested by user")
 func MustParse(dest ...interface{}) *Parser {
 	p, err := NewParser(Config{}, dest...)
 	if err != nil {
-		fmt.Println(err)
+		fmt.Fprintln(stdout, err)
 		osExit(-1)
 		return nil // just in case osExit was monkey-patched
 	}
@@ -88,10 +85,10 @@ func MustParse(dest ...interface{}) *Parser {
 	err = p.Parse(flags())
 	switch {
 	case err == ErrHelp:
-		p.writeHelpForCommand(os.Stdout, p.lastCmd)
+		p.writeHelpForCommand(stdout, p.lastCmd)
 		osExit(0)
 	case err == ErrVersion:
-		fmt.Println(p.version)
+		fmt.Fprintln(stdout, p.version)
 		osExit(0)
 	case err != nil:
 		p.failWithCommand(err.Error(), p.lastCmd)
@@ -688,15 +685,7 @@ func (p *Parser) val(dest path) reflect.Value {
 			v = v.Elem()
 		}
 
-		next := v.FieldByIndex(field.Index)
+		v = v.FieldByIndex(field.Index)
-		if !next.IsValid() {
-			// it is appropriate to panic here because this can only happen due to
-			// an internal bug in this library (since we construct the path ourselves
-			// by reflecting on the same struct)
-			panic(fmt.Errorf("error resolving path %v: %v has no field named %v",
-				dest.fields, v.Type(), field))
-		}
-		v = next
 	}
 	return v
 }
@@ -723,15 +712,3 @@ func findSubcommand(cmds []*command, name string) *command {
 	}
 	return nil
 }
-
-// isZero returns true if v contains the zero value for its type
-func isZero(v reflect.Value) bool {
-	t := v.Type()
-	if t.Kind() == reflect.Slice || t.Kind() == reflect.Map {
-		return v.IsNil()
-	}
-	if !t.Comparable() {
-		return false
-	}
-	return v.Interface() == reflect.Zero(t).Interface()
-}

parse_test.go

@@ -1,6 +1,8 @@
 package arg
 
 import (
+	"bytes"
+	"fmt"
 	"net"
 	"net/mail"
 	"os"
@@ -24,14 +26,34 @@ func parse(cmdline string, dest interface{}) error {
 }
 
 func pparse(cmdline string, dest interface{}) (*Parser, error) {
+	return parseWithEnv(cmdline, nil, dest)
+}
+
+func parseWithEnv(cmdline string, env []string, dest interface{}) (*Parser, error) {
 	p, err := NewParser(Config{}, dest)
 	if err != nil {
 		return nil, err
 	}
+
+	// split the command line
 	var parts []string
 	if len(cmdline) > 0 {
 		parts = strings.Split(cmdline, " ")
 	}
+
+	// split the environment vars
+	for _, s := range env {
+		pos := strings.Index(s, "=")
+		if pos == -1 {
+			return nil, fmt.Errorf("missing equals sign in %q", s)
+		}
+		err := os.Setenv(s[:pos], s[pos+1:])
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	// execute the parser
 	return p, p.Parse(parts)
 }
 
@@ -461,7 +483,7 @@ func TestMissingValueAtEnd(t *testing.T) {
 	assert.Error(t, err)
 }
 
-func TestMissingValueInMIddle(t *testing.T) {
+func TestMissingValueInMiddle(t *testing.T) {
 	var args struct {
 		Foo string
 		Bar string
@@ -546,6 +568,14 @@ func TestNoMoreOptions(t *testing.T) {
 	assert.Equal(t, []string{"abc", "--foo", "xyz"}, args.Bar)
 }
 
+func TestNoMoreOptionsBeforeHelp(t *testing.T) {
+	var args struct {
+		Foo int
+	}
+	err := parse("not_an_integer -- --help", &args)
+	assert.NotEqual(t, ErrHelp, err)
+}
+
 func TestHelpFlag(t *testing.T) {
 	var args struct {
 		Foo string
@@ -633,9 +663,8 @@ func TestEnvironmentVariable(t *testing.T) {
 	var args struct {
 		Foo string `arg:"env"`
 	}
-	setenv(t, "FOO", "bar")
+	_, err := parseWithEnv("", []string{"FOO=bar"}, &args)
-	os.Args = []string{"example"}
+	require.NoError(t, err)
-	MustParse(&args)
 	assert.Equal(t, "bar", args.Foo)
 }
 
@@ -643,8 +672,8 @@ func TestEnvironmentVariableNotPresent(t *testing.T) {
 	var args struct {
 		NotPresent string `arg:"env"`
 	}
-	os.Args = []string{"example"}
+	_, err := parseWithEnv("", nil, &args)
-	MustParse(&args)
+	require.NoError(t, err)
 	assert.Equal(t, "", args.NotPresent)
 }
 
@@ -652,9 +681,8 @@ func TestEnvironmentVariableOverrideName(t *testing.T) {
 	var args struct {
 		Foo string `arg:"env:BAZ"`
 	}
-	setenv(t, "BAZ", "bar")
+	_, err := parseWithEnv("", []string{"BAZ=bar"}, &args)
-	os.Args = []string{"example"}
+	require.NoError(t, err)
-	MustParse(&args)
 	assert.Equal(t, "bar", args.Foo)
 }
 
@@ -662,19 +690,16 @@ func TestEnvironmentVariableOverrideArgument(t *testing.T) {
 	var args struct {
 		Foo string `arg:"env"`
 	}
-	setenv(t, "FOO", "bar")
+	_, err := parseWithEnv("--foo zzz", []string{"FOO=bar"}, &args)
-	os.Args = []string{"example", "--foo", "baz"}
+	require.NoError(t, err)
-	MustParse(&args)
+	assert.Equal(t, "zzz", args.Foo)
-	assert.Equal(t, "baz", args.Foo)
 }
 
 func TestEnvironmentVariableError(t *testing.T) {
 	var args struct {
 		Foo int `arg:"env"`
 	}
-	setenv(t, "FOO", "bar")
+	_, err := parseWithEnv("", []string{"FOO=bar"}, &args)
-	os.Args = []string{"example"}
-	err := Parse(&args)
 	assert.Error(t, err)
 }
 
@@ -682,9 +707,8 @@ func TestEnvironmentVariableRequired(t *testing.T) {
 	var args struct {
 		Foo string `arg:"env,required"`
 	}
-	setenv(t, "FOO", "bar")
+	_, err := parseWithEnv("", []string{"FOO=bar"}, &args)
-	os.Args = []string{"example"}
+	require.NoError(t, err)
-	MustParse(&args)
 	assert.Equal(t, "bar", args.Foo)
 }
 
@@ -692,8 +716,8 @@ func TestEnvironmentVariableSliceArgumentString(t *testing.T) {
 	var args struct {
 		Foo []string `arg:"env"`
 	}
-	setenv(t, "FOO", `bar,"baz, qux"`)
+	_, err := parseWithEnv("", []string{`FOO=bar,"baz, qux"`}, &args)
-	MustParse(&args)
+	require.NoError(t, err)
 	assert.Equal(t, []string{"bar", "baz, qux"}, args.Foo)
 }
 
@@ -701,8 +725,8 @@ func TestEnvironmentVariableSliceArgumentInteger(t *testing.T) {
 	var args struct {
 		Foo []int `arg:"env"`
 	}
-	setenv(t, "FOO", "1,99")
+	_, err := parseWithEnv("", []string{`FOO=1,99`}, &args)
-	MustParse(&args)
+	require.NoError(t, err)
 	assert.Equal(t, []int{1, 99}, args.Foo)
 }
 
@@ -710,8 +734,8 @@ func TestEnvironmentVariableSliceArgumentFloat(t *testing.T) {
 	var args struct {
 		Foo []float32 `arg:"env"`
 	}
-	setenv(t, "FOO", "1.1,99.9")
+	_, err := parseWithEnv("", []string{`FOO=1.1,99.9`}, &args)
-	MustParse(&args)
+	require.NoError(t, err)
 	assert.Equal(t, []float32{1.1, 99.9}, args.Foo)
 }
 
@@ -719,8 +743,8 @@ func TestEnvironmentVariableSliceArgumentBool(t *testing.T) {
 	var args struct {
 		Foo []bool `arg:"env"`
 	}
-	setenv(t, "FOO", "true,false,0,1")
+	_, err := parseWithEnv("", []string{`FOO=true,false,0,1`}, &args)
-	MustParse(&args)
+	require.NoError(t, err)
 	assert.Equal(t, []bool{true, false, false, true}, args.Foo)
 }
 
@@ -728,8 +752,7 @@ func TestEnvironmentVariableSliceArgumentWrongCsv(t *testing.T) {
 	var args struct {
 		Foo []int `arg:"env"`
 	}
-	setenv(t, "FOO", "1,99\"")
+	_, err := parseWithEnv("", []string{`FOO=1,99\"`}, &args)
-	err := Parse(&args)
 	assert.Error(t, err)
 }
 
@@ -737,8 +760,7 @@ func TestEnvironmentVariableSliceArgumentWrongType(t *testing.T) {
 	var args struct {
 		Foo []bool `arg:"env"`
 	}
-	setenv(t, "FOO", "one,two")
+	_, err := parseWithEnv("", []string{`FOO=one,two`}, &args)
-	err := Parse(&args)
 	assert.Error(t, err)
 }
 
@@ -746,8 +768,8 @@ func TestEnvironmentVariableMap(t *testing.T) {
 	var args struct {
 		Foo map[int]string `arg:"env"`
 	}
-	setenv(t, "FOO", "1=one,99=ninetynine")
+	_, err := parseWithEnv("", []string{`FOO=1=one,99=ninetynine`}, &args)
-	MustParse(&args)
+	require.NoError(t, err)
 	assert.Len(t, args.Foo, 2)
 	assert.Equal(t, "one", args.Foo[1])
 	assert.Equal(t, "ninetynine", args.Foo[99])
@@ -1299,3 +1321,70 @@ func TestUnexportedFieldsSkipped(t *testing.T) {
 	_, err := NewParser(Config{}, &args)
 	require.NoError(t, err)
 }
+
+func TestMustParseInvalidParser(t *testing.T) {
+	originalExit := osExit
+	originalStdout := stdout
+	defer func() {
+		osExit = originalExit
+		stdout = originalStdout
+	}()
+
+	var exitCode int
+	osExit = func(code int) { exitCode = code }
+	stdout = &bytes.Buffer{}
+
+	var args struct {
+		CannotParse struct{}
+	}
+	parser := MustParse(&args)
+	assert.Nil(t, parser)
+	assert.Equal(t, -1, exitCode)
+}
+
+func TestMustParsePrintsHelp(t *testing.T) {
+	originalExit := osExit
+	originalStdout := stdout
+	originalArgs := os.Args
+	defer func() {
+		osExit = originalExit
+		stdout = originalStdout
+		os.Args = originalArgs
+	}()
+
+	var exitCode *int
+	osExit = func(code int) { exitCode = &code }
+	os.Args = []string{"someprogram", "--help"}
+	stdout = &bytes.Buffer{}
+
+	var args struct{}
+	parser := MustParse(&args)
+	assert.NotNil(t, parser)
+	require.NotNil(t, exitCode)
+	assert.Equal(t, 0, *exitCode)
+}
+
+func TestMustParsePrintsVersion(t *testing.T) {
+	originalExit := osExit
+	originalStdout := stdout
+	originalArgs := os.Args
+	defer func() {
+		osExit = originalExit
+		stdout = originalStdout
+		os.Args = originalArgs
+	}()
+
+	var exitCode *int
+	osExit = func(code int) { exitCode = &code }
+	os.Args = []string{"someprogram", "--version"}
+
+	var b bytes.Buffer
+	stdout = &b
+
+	var args versioned
+	parser := MustParse(&args)
+	require.NotNil(t, parser)
+	require.NotNil(t, exitCode)
+	assert.Equal(t, 0, *exitCode)
+	assert.Equal(t, "example 3.2.1\n", b.String())
+}

reflect.go

@@ -94,3 +94,15 @@ func isExported(field string) bool {
 	r, _ := utf8.DecodeRuneInString(field) // returns RuneError for empty string or invalid UTF8
 	return unicode.IsLetter(r) && unicode.IsUpper(r)
 }
+
+// isZero returns true if v contains the zero value for its type
+func isZero(v reflect.Value) bool {
+	t := v.Type()
+	if t.Kind() == reflect.Slice || t.Kind() == reflect.Map {
+		return v.IsNil()
+	}
+	if !t.Comparable() {
+		return false
+	}
+	return v.Interface() == reflect.Zero(t).Interface()
+}

reflect_test.go

@@ -89,3 +89,24 @@ func TestCardinalityString(t *testing.T) {
 	assert.Equal(t, "unsupported", unsupported.String())
 	assert.Equal(t, "unknown(42)", cardinality(42).String())
 }
+
+func TestIsZero(t *testing.T) {
+	var zero int
+	var notZero = 3
+	var nilSlice []int
+	var nonNilSlice = []int{1, 2, 3}
+	var nilMap map[string]string
+	var nonNilMap = map[string]string{"foo": "bar"}
+	var uncomparable = func() {}
+
+	assert.True(t, isZero(reflect.ValueOf(zero)))
+	assert.False(t, isZero(reflect.ValueOf(notZero)))
+
+	assert.True(t, isZero(reflect.ValueOf(nilSlice)))
+	assert.False(t, isZero(reflect.ValueOf(nonNilSlice)))
+
+	assert.True(t, isZero(reflect.ValueOf(nilMap)))
+	assert.False(t, isZero(reflect.ValueOf(nonNilMap)))
+
+	assert.False(t, isZero(reflect.ValueOf(uncomparable)))
+}

subcommand_test.go

@@ -1,6 +1,7 @@
 package arg
 
 import (
+	"reflect"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -48,6 +49,17 @@ func TestMinimalSubcommand(t *testing.T) {
 	assert.Equal(t, []string{"list"}, p.SubcommandNames())
 }
 
+func TestSubcommandNamesBeforeParsing(t *testing.T) {
+	type listCmd struct{}
+	var args struct {
+		List *listCmd `arg:"subcommand"`
+	}
+	p, err := NewParser(Config{}, &args)
+	require.NoError(t, err)
+	assert.Nil(t, p.Subcommand())
+	assert.Nil(t, p.SubcommandNames())
+}
+
 func TestNoSuchSubcommand(t *testing.T) {
 	type listCmd struct {
 	}
@@ -179,6 +191,36 @@ func TestSubcommandsWithOptions(t *testing.T) {
 	}
 }
 
+func TestSubcommandsWithEnvVars(t *testing.T) {
+	type getCmd struct {
+		Name string `arg:"env"`
+	}
+	type listCmd struct {
+		Limit int `arg:"env"`
+	}
+	type cmd struct {
+		Verbose bool
+		Get     *getCmd  `arg:"subcommand"`
+		List    *listCmd `arg:"subcommand"`
+	}
+
+	{
+		var args cmd
+		setenv(t, "LIMIT", "123")
+		err := parse("list", &args)
+		require.NoError(t, err)
+		require.NotNil(t, args.List)
+		assert.Equal(t, 123, args.List.Limit)
+	}
+
+	{
+		var args cmd
+		setenv(t, "LIMIT", "not_an_integer")
+		err := parse("list", &args)
+		assert.Error(t, err)
+	}
+}
+
 func TestNestedSubcommands(t *testing.T) {
 	type child struct{}
 	type parent struct {
@@ -353,3 +395,19 @@ func TestSubcommandsWithMultiplePositionals(t *testing.T) {
 		assert.Equal(t, 5, args.Limit)
 	}
 }
+
+func TestValForNilStruct(t *testing.T) {
+	type subcmd struct{}
+	var cmd struct {
+		Sub *subcmd `arg:"subcommand"`
+	}
+
+	p, err := NewParser(Config{}, &cmd)
+	require.NoError(t, err)
+
+	typ := reflect.TypeOf(cmd)
+	subField, _ := typ.FieldByName("Sub")
+
+	v := p.val(path{fields: []reflect.StructField{subField, subField}})
+	assert.False(t, v.IsValid())
+}

usage.go

@@ -11,7 +11,11 @@ import (
 const colWidth = 25
 
 // to allow monkey patching in tests
-var stderr = os.Stderr
+var (
+	stdout io.Writer = os.Stdout
+	stderr io.Writer = os.Stderr
+	osExit           = os.Exit
+)
 
 // Fail prints usage information to stderr and exits with non-zero status
 func (p *Parser) Fail(msg string) {

usage_test.go

@@ -33,9 +33,10 @@ func (n *NameDotName) MarshalText() (text []byte, err error) {
 }
 
 func TestWriteUsage(t *testing.T) {
-	expectedUsage := "Usage: example [--name NAME] [--value VALUE] [--verbose] [--dataset DATASET] [--optimize OPTIMIZE] [--ids IDS] [--values VALUES] [--workers WORKERS] [--testenv TESTENV] [--file FILE] INPUT [OUTPUT [OUTPUT ...]]\n"
+	expectedUsage := "Usage: example [--name NAME] [--value VALUE] [--verbose] [--dataset DATASET] [--optimize OPTIMIZE] [--ids IDS] [--values VALUES] [--workers WORKERS] [--testenv TESTENV] [--file FILE] INPUT [OUTPUT [OUTPUT ...]]"
 
-	expectedHelp := `Usage: example [--name NAME] [--value VALUE] [--verbose] [--dataset DATASET] [--optimize OPTIMIZE] [--ids IDS] [--values VALUES] [--workers WORKERS] [--testenv TESTENV] [--file FILE] INPUT [OUTPUT [OUTPUT ...]]
+	expectedHelp := `
+Usage: example [--name NAME] [--value VALUE] [--verbose] [--dataset DATASET] [--optimize OPTIMIZE] [--ids IDS] [--values VALUES] [--workers WORKERS] [--testenv TESTENV] [--file FILE] INPUT [OUTPUT [OUTPUT ...]]
 
 Positional arguments:
   INPUT
@@ -56,6 +57,7 @@ Options:
   --file FILE, -f FILE   File with mandatory extension [default: scratch.txt]
   --help, -h             display this help and exit
 `
+
 	var args struct {
 		Input    string       `arg:"positional"`
 		Output   []string     `arg:"positional" help:"list of outputs"`
@@ -79,13 +81,13 @@ Options:
 
 	os.Args[0] = "example"
 
-	var usage bytes.Buffer
-	p.WriteUsage(&usage)
-	assert.Equal(t, expectedUsage, usage.String())
-
 	var help bytes.Buffer
 	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp, help.String())
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
 }
 
 type MyEnum int
@@ -99,7 +101,10 @@ func (n *MyEnum) MarshalText() ([]byte, error) {
 }
 
 func TestUsageWithDefaults(t *testing.T) {
-	expectedHelp := `Usage: example [--label LABEL] [--content CONTENT]
+	expectedUsage := "Usage: example [--label LABEL] [--content CONTENT]"
+
+	expectedHelp := `
+Usage: example [--label LABEL] [--content CONTENT]
 
 Options:
   --label LABEL [default: cat]
@@ -118,7 +123,11 @@ Options:
 
 	var help bytes.Buffer
 	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp, help.String())
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
 }
 
 func TestUsageCannotMarshalToString(t *testing.T) {
@@ -132,7 +141,10 @@ func TestUsageCannotMarshalToString(t *testing.T) {
 }
 
 func TestUsageLongPositionalWithHelp_legacyForm(t *testing.T) {
-	expectedHelp := `Usage: example VERYLONGPOSITIONALWITHHELP
+	expectedUsage := "Usage: example VERYLONGPOSITIONALWITHHELP"
+
+	expectedHelp := `
+Usage: example VERYLONGPOSITIONALWITHHELP
 
 Positional arguments:
   VERYLONGPOSITIONALWITHHELP
@@ -145,17 +157,23 @@ Options:
 		VeryLongPositionalWithHelp string `arg:"positional,help:this positional argument is very long but cannot include commas"`
 	}
 
-	p, err := NewParser(Config{}, &args)
+	p, err := NewParser(Config{Program: "example"}, &args)
 	require.NoError(t, err)
 
-	os.Args[0] = "example"
 	var help bytes.Buffer
 	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp, help.String())
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
 }
 
 func TestUsageLongPositionalWithHelp_newForm(t *testing.T) {
-	expectedHelp := `Usage: example VERYLONGPOSITIONALWITHHELP
+	expectedUsage := "Usage: example VERYLONGPOSITIONALWITHHELP"
+
+	expectedHelp := `
+Usage: example VERYLONGPOSITIONALWITHHELP
 
 Positional arguments:
   VERYLONGPOSITIONALWITHHELP
@@ -168,17 +186,23 @@ Options:
 		VeryLongPositionalWithHelp string `arg:"positional" help:"this positional argument is very long, and includes: commas, colons etc"`
 	}
 
-	p, err := NewParser(Config{}, &args)
+	p, err := NewParser(Config{Program: "example"}, &args)
 	require.NoError(t, err)
 
-	os.Args[0] = "example"
 	var help bytes.Buffer
 	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp, help.String())
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
 }
 
 func TestUsageWithProgramName(t *testing.T) {
-	expectedHelp := `Usage: myprogram
+	expectedUsage := "Usage: myprogram"
+
+	expectedHelp := `
+Usage: myprogram
 
 Options:
   --help, -h             display this help and exit
@@ -190,9 +214,14 @@ Options:
 	require.NoError(t, err)
 
 	os.Args[0] = "example"
+
 	var help bytes.Buffer
 	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp, help.String())
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
 }
 
 type versioned struct{}
@@ -203,7 +232,10 @@ func (versioned) Version() string {
 }
 
 func TestUsageWithVersion(t *testing.T) {
-	expectedHelp := `example 3.2.1
+	expectedUsage := "example 3.2.1\nUsage: example"
+
+	expectedHelp := `
+example 3.2.1
 Usage: example
 
 Options:
@@ -216,12 +248,11 @@ Options:
 
 	var help bytes.Buffer
 	p.WriteHelp(&help)
-	actual := help.String()
+	assert.Equal(t, expectedHelp[1:], help.String())
-	if expectedHelp != actual {
+
-		t.Logf("Expected:\n%s", expectedHelp)
+	var usage bytes.Buffer
-		t.Logf("Actual:\n%s", actual)
+	p.WriteUsage(&usage)
-		t.Fail()
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
-	}
 }
 
 type described struct{}
@@ -232,7 +263,10 @@ func (described) Description() string {
 }
 
 func TestUsageWithDescription(t *testing.T) {
-	expectedHelp := `this program does this and that
+	expectedUsage := "Usage: example"
+
+	expectedHelp := `
+this program does this and that
 Usage: example
 
 Options:
@@ -244,16 +278,18 @@ Options:
 
 	var help bytes.Buffer
 	p.WriteHelp(&help)
-	actual := help.String()
+	assert.Equal(t, expectedHelp[1:], help.String())
-	if expectedHelp != actual {
+
-		t.Logf("Expected:\n%s", expectedHelp)
+	var usage bytes.Buffer
-		t.Logf("Actual:\n%s", actual)
+	p.WriteUsage(&usage)
-		t.Fail()
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
-	}
 }
 
 func TestRequiredMultiplePositionals(t *testing.T) {
-	expectedHelp := `Usage: example REQUIREDMULTIPLE [REQUIREDMULTIPLE ...]
+	expectedUsage := "Usage: example REQUIREDMULTIPLE [REQUIREDMULTIPLE ...]"
+
+	expectedHelp := `
+Usage: example REQUIREDMULTIPLE [REQUIREDMULTIPLE ...]
 
 Positional arguments:
   REQUIREDMULTIPLE       required multiple positional
@@ -270,11 +306,18 @@ Options:
 
 	var help bytes.Buffer
 	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp, help.String())
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
 }
 
 func TestUsageWithNestedSubcommands(t *testing.T) {
-	expectedHelp := `Usage: example child nested [--enable] OUTPUT
+	expectedUsage := "Usage: example child nested [--enable] OUTPUT"
+
+	expectedHelp := `
+Usage: example child nested [--enable] OUTPUT
 
 Positional arguments:
   OUTPUT
@@ -307,11 +350,18 @@ Global options:
 
 	var help bytes.Buffer
 	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp, help.String())
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
 }
 
 func TestUsageWithoutLongNames(t *testing.T) {
-	expectedHelp := `Usage: example [-a PLACEHOLDER] -b SHORTONLY2
+	expectedUsage := "Usage: example [-a PLACEHOLDER] -b SHORTONLY2"
+
+	expectedHelp := `
+Usage: example [-a PLACEHOLDER] -b SHORTONLY2
 
 Options:
   -a PLACEHOLDER         some help [default: some val]
@@ -324,13 +374,21 @@ Options:
 	}
 	p, err := NewParser(Config{Program: "example"}, &args)
 	assert.NoError(t, err)
+
 	var help bytes.Buffer
 	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp, help.String())
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
 }
 
 func TestUsageWithShortFirst(t *testing.T) {
-	expectedHelp := `Usage: example [-c CAT] [--dog DOG]
+	expectedUsage := "Usage: example [-c CAT] [--dog DOG]"
+
+	expectedHelp := `
+Usage: example [-c CAT] [--dog DOG]
 
 Options:
   -c CAT
@@ -343,13 +401,21 @@ Options:
 	}
 	p, err := NewParser(Config{Program: "example"}, &args)
 	assert.NoError(t, err)
+
 	var help bytes.Buffer
 	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp, help.String())
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
 }
 
 func TestUsageWithEnvOptions(t *testing.T) {
-	expectedHelp := `Usage: example [-s SHORT]
+	expectedUsage := "Usage: example [-s SHORT]"
+
+	expectedHelp := `
+Usage: example [-s SHORT]
 
 Options:
   -s SHORT [env: SHORT]
@@ -363,7 +429,42 @@ Options:
 
 	p, err := NewParser(Config{Program: "example"}, &args)
 	assert.NoError(t, err)
+
 	var help bytes.Buffer
 	p.WriteHelp(&help)
-	assert.Equal(t, expectedHelp, help.String())
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
+}
+
+func TestFail(t *testing.T) {
+	originalStderr := stderr
+	originalExit := osExit
+	defer func() {
+		stderr = originalStderr
+		osExit = originalExit
+	}()
+
+	var b bytes.Buffer
+	stderr = &b
+
+	var exitCode int
+	osExit = func(code int) { exitCode = code }
+
+	expectedStdout := `
+Usage: example [--foo FOO]
+error: something went wrong
+`
+
+	var args struct {
+		Foo int
+	}
+	p, err := NewParser(Config{Program: "example"}, &args)
+	require.NoError(t, err)
+	p.Fail("something went wrong")
+
+	assert.Equal(t, expectedStdout[1:], b.String())
+	assert.Equal(t, -1, exitCode)
 }