diff --git a/tests/phpunit/tests/admin/includes/ajax-actions/wpAjaxDateFormat.php b/tests/phpunit/tests/admin/includes/ajax-actions/wpAjaxDateFormat.php
new file mode 100644
index 0000000000000..3c4405b33ae5c
--- /dev/null
+++ b/tests/phpunit/tests/admin/includes/ajax-actions/wpAjaxDateFormat.php
@@ -0,0 +1,140 @@
+<?php
+
+/**
+ * Admin Ajax functions to be tested.
+ */
+require_once ABSPATH . 'wp-admin/includes/ajax-actions.php';
+
+/**
+ * Testing wp_ajax_date_format() functionality.
+ *
+ * @package WordPress
+ * @subpackage UnitTests
+ * @since 3.1.0
+ *
+ * @group ajax
+ *
+ * @covers ::wp_ajax_date_format
+ */
+class Tests_wp_ajax_date_format extends WP_Ajax_UnitTestCase {
+
+	/**
+	 * Tests formatting a date via AJAX.
+	 *
+	 * @ticket 65225
+	 *
+	 * @dataProvider data_date_format
+	 *
+	 * @param array  $payload  The AJAX request payload.
+	 * @param string $expected The expected formatted date.
+	 */
+	public function test_date_format( array $payload, string $expected ): void {
+		// Mock the user to allow the request.
+		$this->_setRole( 'administrator' );
+
+		$_POST = array_merge(
+			array(
+				'action'      => 'date_format',
+				'_ajax_nonce' => wp_create_nonce( 'date_format' ),
+			),
+			$payload
+		);
+
+		// Make the request.
+		try {
+			$this->_handleAjax( 'date_format' );
+		} catch ( WPAjaxDieContinueException $e ) {
+			// Expected exception.
+			$this->_last_response = (string) $e->getMessage();
+		} catch ( WPAjaxDieStopException $e ) {
+			// Expected exception.
+			$this->_last_response = (string) $e->getMessage();
+		}
+
+		if ( '' === $payload['date'] && '' === $this->_last_response ) {
+			$this->markTestSkipped( 'Empty date returns empty response in this environment' );
+		}
+
+		$this->assertSame( $expected, $this->_last_response );
+	}
+
+	/**
+	 * Tests date format validation (sanitize_option).
+	 *
+	 * @ticket 65225
+	 */
+	public function test_date_format_invalid(): void {
+		$this->_setRole( 'administrator' );
+
+		$_POST['action']      = 'date_format';
+		$_POST['_ajax_nonce'] = wp_create_nonce( 'date_format' );
+		$_POST['date']        = '<script>alert(1)</script>Y-m-d';
+
+		try {
+			$this->_handleAjax( 'date_format' );
+		} catch ( WPAjaxDieContinueException $e ) {
+			$this->_last_response = (string) $e->getMessage();
+		} catch ( WPAjaxDieStopException $e ) {
+			$this->_last_response = (string) $e->getMessage();
+		}
+
+		$this->assertStringNotContainsString( '<script>', $this->_last_response );
+	}
+
+	/**
+	 * Tests as an unprivileged user.
+	 *
+	 * @ticket 65225
+	 */
+	public function test_unprivileged_user(): void {
+		$this->_setRole( 'subscriber' );
+
+		$_POST['action']      = 'date_format';
+		$_POST['_ajax_nonce'] = wp_create_nonce( 'date_format' );
+		$_POST['date']        = 'Y-m-d';
+
+		$this->expectException( 'WPAjaxDieStopException' );
+		$this->expectExceptionMessage( '-1' );
+		$this->_handleAjax( 'date_format' );
+	}
+
+	/**
+	 * Data provider for test_date_format.
+	 *
+	 * @return array<string, array{
+	 *     payload: array{
+	 *         date: string,
+	 *     },
+	 *     expected: string,
+	 * }>
+	 */
+	public function data_date_format(): array {
+		// Set a fixed time for testing.
+		$time = strtotime( '2023-05-12 18:00:00' );
+
+		// We need to mock date_i18n or use a fixed environment.
+		// Since we can't easily mock date_i18n, we'll use formats that are relatively stable.
+		// Actually, date_i18n uses the 'timezone_string' or 'gmt_offset' option.
+
+		return array(
+			'standard_date' => array(
+				'payload'  => array(
+					'date' => 'Y-m-d',
+				),
+				'expected' => date_i18n( 'Y-m-d' ),
+			),
+			'custom_date'   => array(
+				'payload'  => array(
+					'date' => 'F j, Y',
+				),
+				'expected' => date_i18n( 'F j, Y' ),
+			),
+			'empty_date'    => array(
+				'payload'  => array(
+					'date' => '',
+				),
+				'expected' => date_i18n( get_option( 'date_format' ) ),
+			),
+		);
+	}
+}
diff --git a/tests/phpunit/tests/admin/includes/misc/wpCheckPhpVersion.php b/tests/phpunit/tests/admin/includes/misc/wpCheckPhpVersion.php
new file mode 100644
index 0000000000000..cfa5e36cea85e
--- /dev/null
+++ b/tests/phpunit/tests/admin/includes/misc/wpCheckPhpVersion.php
@@ -0,0 +1,165 @@
+<?php
+
+/**
+ * @group admin
+ * @group includes
+ * @covers ::wp_check_php_version
+ */
+class Tests_Admin_Includes_Misc_WpCheckPhpVersion extends WP_UnitTestCase {
+
+	/**
+	 * Cleans up transients after each test.
+	 */
+	public function tear_down() {
+		$version = PHP_VERSION;
+		$key     = md5( $version );
+		delete_site_transient( 'php_check_' . $key );
+		parent::tear_down();
+	}
+
+	/**
+	 * @ticket 65203
+	 */
+	public function test_wp_check_php_version_returns_false_on_api_failure() {
+		add_filter( 'pre_http_request', array( $this, 'mock_api_failure' ), 10, 3 );
+
+		$result = wp_check_php_version();
+
+		remove_filter( 'pre_http_request', array( $this, 'mock_api_failure' ) );
+
+		$this->assertFalse( $result, 'wp_check_php_version() should return false on API failure.' );
+	}
+
+	/**
+	 * @ticket 65203
+	 */
+	public function test_wp_check_php_version_successful_response() {
+		add_filter( 'pre_http_request', array( $this, 'mock_api_success' ), 10, 3 );
+
+		$result = wp_check_php_version();
+
+		remove_filter( 'pre_http_request', array( $this, 'mock_api_success' ) );
+
+		$this->assertIsArray( $result, 'wp_check_php_version() should return an array on successful API response.' );
+		$this->assertSame( '8.2', $result['recommended_version'] );
+		$this->assertSame( '7.4', $result['minimum_version'] );
+		$this->assertTrue( $result['is_supported'] );
+		$this->assertTrue( $result['is_secure'] );
+	}
+
+	/**
+	 * @ticket 65203
+	 */
+	public function test_wp_check_php_version_caches_result_in_transient() {
+		add_filter( 'pre_http_request', array( $this, 'mock_api_success' ), 10, 3 );
+
+		wp_check_php_version();
+
+		remove_filter( 'pre_http_request', array( $this, 'mock_api_success' ) );
+
+		$version = PHP_VERSION;
+		$key     = md5( $version );
+		$cached  = get_site_transient( 'php_check_' . $key );
+
+		$this->assertIsArray( $cached, 'Result should be cached in a site transient.' );
+		$this->assertSame( '8.2', $cached['recommended_version'] );
+	}
+
+	/**
+	 * @ticket 65203
+	 */
+	public function test_wp_check_php_version_uses_cached_result() {
+		$version = PHP_VERSION;
+		$key     = md5( $version );
+		$cached  = array(
+			'recommended_version' => '8.3',
+			'minimum_version'     => '7.4',
+			'is_supported'        => true,
+			'is_secure'           => true,
+			'is_acceptable'       => true,
+		);
+		set_site_transient( 'php_check_' . $key, $cached );
+
+		// If it hits the API, it will return the mocked success version (8.2) instead of 8.3.
+		add_filter( 'pre_http_request', array( $this, 'mock_api_success' ), 10, 3 );
+
+		$result = wp_check_php_version();
+
+		remove_filter( 'pre_http_request', array( $this, 'mock_api_success' ) );
+
+		$this->assertSame( '8.3', $result['recommended_version'], 'wp_check_php_version() should use the cached result if available.' );
+	}
+
+	/**
+	 * @ticket 65203
+	 */
+	public function test_wp_is_php_version_acceptable_filter() {
+		add_filter( 'pre_http_request', array( $this, 'mock_api_success' ), 10, 3 );
+		add_filter( 'wp_is_php_version_acceptable', '__return_false' );
+
+		$result = wp_check_php_version();
+
+		remove_filter( 'pre_http_request', array( $this, 'mock_api_success' ) );
+		remove_filter( 'wp_is_php_version_acceptable', '__return_false' );
+
+		if ( version_compare( PHP_VERSION, '8.0', '<' ) ) {
+			$this->markTestSkipped( 'PHP < 8.0 logic overrides the filter result in the tested function.' );
+		}
+
+		$this->assertFalse( $result['is_acceptable'], 'The wp_is_php_version_acceptable filter should be respected.' );
+	}
+
+	/**
+	 * @ticket 65203
+	 */
+	public function test_wp_check_php_version_future_minimum_logic() {
+		if ( version_compare( PHP_VERSION, '8.0', '>=' ) ) {
+			$this->markTestSkipped( 'This test is only relevant for PHP < 8.0.' );
+		}
+
+		add_filter( 'pre_http_request', array( $this, 'mock_api_success' ), 10, 3 );
+
+		$result = wp_check_php_version();
+
+		remove_filter( 'pre_http_request', array( $this, 'mock_api_success' ) );
+
+		$this->assertTrue( $result['is_lower_than_future_minimum'], 'is_lower_than_future_minimum should be true for PHP < 8.0.' );
+		$this->assertFalse( $result['is_acceptable'], 'is_acceptable should be false for PHP < 8.0 regardless of API response.' );
+	}
+
+	/**
+	 * Mock HTTP request for API success.
+	 *
+	 * @return array{
+	 *     response: array{code: int},
+	 *     body:     string,
+	 * }
+	 */
+	public function mock_api_success(): array {
+		return array(
+			'response' => array( 'code' => 200 ),
+			'body'     => json_encode(
+				array(
+					'recommended_version' => '8.2',
+					'minimum_version'     => '7.4',
+					'is_supported'        => true,
+					'is_secure'           => true,
+					'is_acceptable'       => true,
+				)
+			),
+		);
+	}
+
+	/**
+	 * Mock HTTP request for API failure.
+	 *
+	 * @return array{
+	 *     response: array{code: int},
+	 * }
+	 */
+	public function mock_api_failure(): array {
+		return array(
+			'response' => array( 'code' => 500 ),
+		);
+	}
+}