Issue #3502218: Create a new Unit test for RangeValidator validation plugin

Related to #3502218

tests/src/Unit/Validators/RangeValidatorTest.php

+<?php
+
+namespace Drupal\Tests\fapi_validation\Unit\Validators;
+
+use Drupal\fapi_validation\Plugin\FapiValidationValidator\RangeValidator;
+use Drupal\fapi_validation\Validator;
+
+/**
+ * Tests Range Validator.
+ *
+ * @group fapi_validation
+ * @group fapi_validation_validators
+ */
+class RangeValidatorTest extends BaseValidator {
+
+  /**
+   * Numeric validation.
+   *
+   * @var \Drupal\fapi_validation\FapiValidationValidatorsInterface
+   */
+  protected $plugin;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setUp(): void {
+    parent::setUp();
+
+    $this->plugin = new RangeValidator();
+  }
+
+  /**
+   * Testing valid string.
+   */
+  public function testValidString() {
+    $validator = new Validator('range[5, 100]', '95');
+
+    $this->assertTrue($this->plugin->validate($validator, [], $this->decoratedFormState));
+  }
+
+  /**
+   * Testing invalid string.
+   */
+  public function testInvalidString() {
+    $validator = new Validator('range[5, 10]', '3');
+
+    $this->assertFalse($this->plugin->validate($validator, [], $this->decoratedFormState));
+  }
+
+}