fs: create fs.Enum for easy creation of parameters from a list of choices

fs/enum_test.go

@@ -0,0 +1,139 @@
+package fs
+
+import (
+	"encoding/json"
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+type choices struct{}
+
+func (choices) Choices() []string {
+	return []string{
+		choiceA: "A",
+		choiceB: "B",
+		choiceC: "C",
+	}
+}
+
+type choice = Enum[choices]
+
+const (
+	choiceA choice = iota
+	choiceB
+	choiceC
+)
+
+// Check it satisfies the interfaces
+var (
+	_ flagger   = (*choice)(nil)
+	_ flaggerNP = choice(0)
+)
+
+func TestEnumString(t *testing.T) {
+	for _, test := range []struct {
+		in   choice
+		want string
+	}{
+		{choiceA, "A"},
+		{choiceB, "B"},
+		{choiceC, "C"},
+		{choice(100), "Unknown(100)"},
+	} {
+		got := test.in.String()
+		assert.Equal(t, test.want, got)
+	}
+}
+
+func TestEnumType(t *testing.T) {
+	assert.Equal(t, "A|B|C", choiceA.Type())
+}
+
+// Enum with Type() on the choices
+type choicestype struct{}
+
+func (choicestype) Choices() []string {
+	return []string{}
+}
+
+func (choicestype) Type() string {
+	return "potato"
+}
+
+type choicetype = Enum[choicestype]
+
+func TestEnumTypeWithFunction(t *testing.T) {
+	assert.Equal(t, "potato", choicetype(0).Type())
+}
+
+func TestEnumHelp(t *testing.T) {
+	assert.Equal(t, "A, B, C", choice(0).Help())
+}
+
+func TestEnumSet(t *testing.T) {
+	for _, test := range []struct {
+		in   string
+		want choice
+		err  bool
+	}{
+		{"A", choiceA, false},
+		{"B", choiceB, false},
+		{"C", choiceC, false},
+		{"D", choice(100), true},
+	} {
+		var got choice
+		err := got.Set(test.in)
+		if test.err {
+			require.Error(t, err)
+		} else {
+			require.NoError(t, err)
+			assert.Equal(t, test.want, got)
+		}
+	}
+}
+
+func TestEnumScan(t *testing.T) {
+	var v choice
+	n, err := fmt.Sscan(" A ", &v)
+	require.NoError(t, err)
+	assert.Equal(t, 1, n)
+	assert.Equal(t, choiceA, v)
+}
+
+func TestEnumUnmarshalJSON(t *testing.T) {
+	for _, test := range []struct {
+		in   string
+		want choice
+		err  bool
+	}{
+		{`"A"`, choiceA, false},
+		{`"B"`, choiceB, false},
+		{`"D"`, choice(0), true},
+	} {
+		var got choice
+		err := json.Unmarshal([]byte(test.in), &got)
+		if test.err {
+			require.Error(t, err, test.in)
+		} else {
+			require.NoError(t, err, test.in)
+		}
+		assert.Equal(t, test.want, got, test.in)
+	}
+}
+
+func TestEnumMarshalJSON(t *testing.T) {
+	for _, test := range []struct {
+		in   choice
+		want string
+	}{
+		{choiceA, `"A"`},
+		{choiceB, `"B"`},
+	} {
+		got, err := json.Marshal(&test.in)
+		require.NoError(t, err)
+		assert.Equal(t, test.want, string(got), fmt.Sprintf("%#v", test.in))
+	}
+}