Consolidate PHPUnit tests into tests/phpunit directory

Move test-admin.php and test-core.php from tests/ to tests/phpunit/
to match phpunit.xml configuration which only scans tests/phpunit/.

This fixes PHPUnit test discovery issues where tests were being
skipped because they were in the wrong directory.

All test files now in: tests/phpunit/
- test-admin.php
- test-core.php
- test-multisite.php
- bootstrap.php

🤖 Generated with [Qoder][https://qoder.com]

tests/phpunit/test-core.php

@@ -0,0 +1,62 @@
+<?php
+/**
+ * Class CoreTest
+ *
+ * @package WPALLSTARS\PluginStarterTemplate
+ */
+
+use WPALLSTARS\PluginStarterTemplate\Core;
+
+/**
+ * Core test case.
+ */
+class CoreTest extends \WP_Mock\Tools\TestCase {
+
+    /**
+     * Test instance
+     *
+     * @var Core
+     */
+    private $core;
+
+    /**
+     * Set up the test environment.
+     */
+    public function setUp(): void
+    {
+        parent::setUp();
+
+        // Set up mocks
+        WP_Mock::setUp();
+
+        // Create instance of Core class
+        $this->core = new Core();
+    }
+
+    /**
+     * Tear down the test environment.
+     */
+    public function tearDown(): void
+    {
+        WP_Mock::tearDown();
+        parent::tearDown();
+    }
+
+    /**
+     * Test constructor
+     */
+    public function test_constructor() {
+        // Verify that the constructor initializes hooks
+        $this->assertInstanceOf(Core::class, $this->core);
+    }
+
+    /**
+     * Test example method
+     */
+    public function test_filter_content() {
+        $content = 'Test content';
+
+        // Test that filter_content returns the content
+        $this->assertEquals($content, $this->core->filter_content($content));
+    }
+}