Added PhpUnit tests

Author: WalterWoshid

.gitignore

@@ -4,3 +4,7 @@
 # Composer
 vendor/
 composer.lock
+
+# PHPUnit
+.phpunit.result.cache
+tests/coverage/

composer.json

@@ -17,12 +17,24 @@
         "trait",
         "php"
     ],
+    "scripts": {
+        "test": "phpunit",
+        "test-coverage": "phpunit --coverage-html tests/coverage"
+    },
     "require": {
         "php": ">=8.0"
     },
+    "require-dev": {
+        "phpunit/phpunit": ">=9.0"
+    },
     "autoload": {
         "psr-4": {
             "Okapi\\Singleton\\": "src/"
         }
+    },
+    "autoload-dev": {
+        "psr-4": {
+            "Okapi\\Singleton\\Tests\\": "tests/"
+        }
     }
 }

phpunit.xml

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:noNamespaceSchemaLocation="vendor/phpunit/phpunit/phpunit.xsd"
+    colors="true"
+>
+  <testsuites>
+    <testsuite name="Tests">
+      <directory>tests/</directory>
+    </testsuite>
+  </testsuites>
+
+  <coverage>
+    <include>
+      <directory suffix=".php">src/</directory>
+    </include>
+  </coverage>
+</phpunit>

tests/SingletonTest.php

@@ -0,0 +1,49 @@
+<?php
+
+namespace Okapi\Singleton\Tests;
+
+use Okapi\Singleton\Exceptions\AlreadyInitializedException;
+use Okapi\Singleton\Exceptions\NotInitializedException;
+use Okapi\Singleton\Tests\Stub\GovernmentOfUSA;
+use PHPUnit\Framework\TestCase;
+
+class SingletonTest extends TestCase
+{
+    public function testEnsureAlreadyInitializedException(): void
+    {
+        $this->expectException(NotInitializedException::class);
+
+        GovernmentOfUSA::takeOverTheWorld();
+    }
+
+    public function testIsInitialized(): void
+    {
+        $initialized = GovernmentOfUSA::isInitialized();
+        $this->assertFalse($initialized);
+
+        $government = GovernmentOfUSA::getInstance();
+        $this->assertInstanceOf(GovernmentOfUSA::class, $government);
+
+        // Should be false, because the instance should initialize itself
+        $initialized = GovernmentOfUSA::isInitialized();
+        $this->assertFalse($initialized);
+
+        GovernmentOfUSA::register();
+        $initialized = GovernmentOfUSA::isInitialized();
+        $this->assertTrue($initialized);
+    }
+
+    public function testEnsureNotAlreadyInitialized(): void
+    {
+        $this->expectException(AlreadyInitializedException::class);
+
+        GovernmentOfUSA::register();
+    }
+
+    public function testEnsureAlreadyInitialized(): void
+    {
+        GovernmentOfUSA::takeOverTheWorld();
+
+        $this->expectNotToPerformAssertions();
+    }
+}

tests/Stub/GovernmentOfUSA.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace Okapi\Singleton\Tests\Stub;
+
+use Okapi\Singleton\Singleton;
+
+class GovernmentOfUSA
+{
+    use Singleton;
+
+    public static function register(): void
+    {
+        $instance = self::getInstance();
+
+        $instance->ensureNotAlreadyInitialized();
+
+        $instance->setInitialized();
+    }
+
+    public static function takeOverTheWorld(): void
+    {
+        $instance = self::getInstance();
+
+        $instance->ensureAlreadyInitialized();
+    }
+}