Add unit test case for IsBoolValue() implementing a tri-state flag (true/false/maybe)

Signed-off-by: Filipe Brandenburger <filbranden@google.com>

bool_test.go

diff --git a/bool_test.go b/bool_test.go
new file mode 100644
index 0000000..72a12be
--- /dev/null
+++ b/bool_test.go
@@ -0,0 +1,163 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package pflag_test
+
+import (
+	"fmt"
+	"strconv"
+	"testing"
+
+	. "github.com/ogier/pflag"
+)
+
+// This value can be a boolean ("true", "false") or "maybe"
+type triStateValue int
+
+const (
+	triStateFalse triStateValue = 0
+	triStateTrue  triStateValue = 1
+	triStateMaybe triStateValue = 2
+)
+
+const strTriStateMaybe = "maybe"
+
+func (v *triStateValue) IsBoolFlag() bool {
+	return true
+}
+
+func (v *triStateValue) Get() interface{} {
+	return triStateValue(*v)
+}
+
+func (v *triStateValue) Set(s string) error {
+	if s == strTriStateMaybe {
+		*v = triStateMaybe
+		return nil
+	}
+	boolVal, err := strconv.ParseBool(s)
+	if boolVal {
+		*v = triStateTrue
+	} else {
+		*v = triStateFalse
+	}
+	return err
+}
+
+func (v *triStateValue) String() string {
+	if *v == triStateMaybe {
+		return strTriStateMaybe
+	}
+	return fmt.Sprintf("%v", bool(*v == triStateTrue))
+}
+
+// The type of the flag as requred by the pflag.Value interface
+func (v *triStateValue) Type() string {
+	return "version"
+}
+
+func setUpFlagSet(tristate *triStateValue) *FlagSet {
+	f := NewFlagSet("test", ContinueOnError)
+	*tristate = triStateFalse
+	f.VarP(tristate, "tristate", "t", "tristate value (true, maybe or false)")
+	return f
+}
+
+func TestExplicitTrue(t *testing.T) {
+	var tristate triStateValue
+	f := setUpFlagSet(&tristate)
+	err := f.Parse([]string{"--tristate=true"})
+	if err != nil {
+		t.Fatal("expected no error; got", err)
+	}
+	if tristate != triStateTrue {
+		t.Fatal("expected", triStateTrue, "(triStateTrue) but got", tristate, "instead")
+	}
+}
+
+func TestImplicitTrue(t *testing.T) {
+	var tristate triStateValue
+	f := setUpFlagSet(&tristate)
+	err := f.Parse([]string{"--tristate"})
+	if err != nil {
+		t.Fatal("expected no error; got", err)
+	}
+	if tristate != triStateTrue {
+		t.Fatal("expected", triStateTrue, "(triStateTrue) but got", tristate, "instead")
+	}
+}
+
+func TestShortFlag(t *testing.T) {
+	var tristate triStateValue
+	f := setUpFlagSet(&tristate)
+	err := f.Parse([]string{"-t"})
+	if err != nil {
+		t.Fatal("expected no error; got", err)
+	}
+	if tristate != triStateTrue {
+		t.Fatal("expected", triStateTrue, "(triStateTrue) but got", tristate, "instead")
+	}
+}
+
+func TestShortFlagExtraArgument(t *testing.T) {
+	var tristate triStateValue
+	f := setUpFlagSet(&tristate)
+	// The"maybe"turns into an arg, since short boolean options will only do true/false
+	err := f.Parse([]string{"-t", "maybe"})
+	if err != nil {
+		t.Fatal("expected no error; got", err)
+	}
+	if tristate != triStateTrue {
+		t.Fatal("expected", triStateTrue, "(triStateTrue) but got", tristate, "instead")
+	}
+	args := f.Args()
+	if len(args) != 1 || args[0] != "maybe" {
+		t.Fatal("expected an extra 'maybe' argument to stick around")
+	}
+}
+
+func TestExplicitMaybe(t *testing.T) {
+	var tristate triStateValue
+	f := setUpFlagSet(&tristate)
+	err := f.Parse([]string{"--tristate=maybe"})
+	if err != nil {
+		t.Fatal("expected no error; got", err)
+	}
+	if tristate != triStateMaybe {
+		t.Fatal("expected", triStateMaybe, "(triStateMaybe) but got", tristate, "instead")
+	}
+}
+
+func TestExplicitFalse(t *testing.T) {
+	var tristate triStateValue
+	f := setUpFlagSet(&tristate)
+	err := f.Parse([]string{"--tristate=false"})
+	if err != nil {
+		t.Fatal("expected no error; got", err)
+	}
+	if tristate != triStateFalse {
+		t.Fatal("expected", triStateFalse, "(triStateFalse) but got", tristate, "instead")
+	}
+}
+
+func TestImplicitFalse(t *testing.T) {
+	var tristate triStateValue
+	f := setUpFlagSet(&tristate)
+	err := f.Parse([]string{})
+	if err != nil {
+		t.Fatal("expected no error; got", err)
+	}
+	if tristate != triStateFalse {
+		t.Fatal("expected", triStateFalse, "(triStateFalse) but got", tristate, "instead")
+	}
+}
+
+func TestInvalidValue(t *testing.T) {
+	var tristate triStateValue
+	f := setUpFlagSet(&tristate)
+	err := f.Parse([]string{"--tristate=invalid"})
+	if err == nil {
+		t.Fatal("expected an error but did not get any, tristate has value", tristate)
+	}
+}