Add Digits validation checker and tests to v2. (#133)

# Describe Request

Add Digits validation checker and tests to v2.

# Change Type

New code.

v2/digits.go

@@ -0,0 +1,42 @@
+// Copyright (c) 2023-2024 Onur Cinar.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+// https://github.com/cinar/checker
+
+package v2
+
+import (
+    "reflect"
+    "unicode"
+)
+
+const (
+    // nameDigits is the name of the digits check.
+    nameDigits = "digits"
+)
+
+var (
+    // ErrNotDigits indicates that the given value is not a valid digits string.
+    ErrNotDigits = NewCheckError("Digits")
+)
+
+// IsDigits checks if the value contains only digit characters.
+func IsDigits(value string) (string, error) {
+    for _, r := range value {
+        if !unicode.IsDigit(r) {
+            return value, ErrNotDigits
+        }
+    }
+    return value, nil
+}
+
+// checkDigits checks if the value contains only digit characters.
+func checkDigits(value reflect.Value) (reflect.Value, error) {
+    _, err := IsDigits(value.Interface().(string))
+    return value, err
+}
+
+// makeDigits makes a checker function for the digits checker.
+func makeDigits(_ string) CheckFunc[reflect.Value] {
+    return checkDigits
+}

v2/digits_test.go

@@ -0,0 +1,76 @@
+// Copyright (c) 2023-2024 Onur Cinar.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+// https://github.com/cinar/checker
+
+package v2_test
+
+import (
+	"fmt"
+	"testing"
+
+	v2 "github.com/cinar/checker/v2"
+)
+
+func ExampleIsDigits() {
+	_, err := v2.IsDigits("123456")
+	if err != nil {
+		fmt.Println(err)
+	}
+}
+
+func TestIsDigitsInvalid(t *testing.T) {
+	_, err := v2.IsDigits("123a456")
+	if err == nil {
+		t.Fatal("expected error")
+	}
+}
+
+func TestIsDigitsValid(t *testing.T) {
+	_, err := v2.IsDigits("123456")
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestCheckDigitsNonString(t *testing.T) {
+	defer FailIfNoPanic(t, "expected panic")
+
+	type Code struct {
+		Value int `checkers:"digits"`
+	}
+
+	code := &Code{}
+
+	v2.CheckStruct(code)
+}
+
+func TestCheckDigitsInvalid(t *testing.T) {
+	type Code struct {
+		Value string `checkers:"digits"`
+	}
+
+	code := &Code{
+		Value: "123a456",
+	}
+
+	_, ok := v2.CheckStruct(code)
+	if ok {
+		t.Fatal("expected error")
+	}
+}
+
+func TestCheckDigitsValid(t *testing.T) {
+	type Code struct {
+		Value string `checkers:"digits"`
+	}
+
+	code := &Code{
+		Value: "123456",
+	}
+
+	_, ok := v2.CheckStruct(code)
+	if !ok {
+		t.Fatal("expected valid")
+	}
+}

v2/maker.go

@@ -19,6 +19,7 @@ var makers = map[string]MakeCheckFunc{
 	nameAlphanumeric: makeAlphanumeric,
 	nameASCII:        makeASCII,
 	nameCIDR:         makeCIDR,
+	nameDigits:       makeDigits,
 	nameMaxLen:       makeMaxLen,
 	nameMinLen:       makeMinLen,
 	nameRequired:     makeRequired,