support multi-module (#4)

* add multimodule
* re-package modules

error/generic_test.go

@@ -0,0 +1,27 @@
+package error
+
+import (
+	"errors"
+	"strconv"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNewGenericError(t *testing.T) {
+	for i, tc := range []struct {
+		arg     []any
+		message string
+	}{
+		{arg: []any{"Foo"}, message: "Dummy: Foo"},
+		{arg: []any{"Foo%s", "Bar"}, message: "Dummy: FooBar"},
+		{arg: []any{errors.New("Error")}, message: "Dummy: Error"},
+		{arg: []any{errors.New("Error"), "Foo"}, message: "Dummy: Foo: Error"},
+		{arg: []any{errors.New("Error"), "Foo%s", "Bar"}, message: "Dummy: FooBar: Error"},
+	} {
+		t.Run(strconv.Itoa(i), func(t *testing.T) {
+			err := newGenericError(ErrDummy, tc.arg...)
+			assert.EqualError(t, err, tc.message)
+		})
+	}
+}