diff --git a/tests/phpunit/tests/functions/wpJsonEncode.php b/tests/phpunit/tests/functions/wpJsonEncode.php
new file mode 100644
index 0000000000000..04716cf200e70
--- /dev/null
+++ b/tests/phpunit/tests/functions/wpJsonEncode.php
@@ -0,0 +1,99 @@
+<?php
+
+/**
+ * Tests the wp_json_encode() function.
+ *
+ * @group functions
+ *
+ * @covers ::wp_json_encode
+ */
+class Tests_Functions_WpJsonEncode extends WP_UnitTestCase {
+
+	/**
+	 * Tests basic JSON encoding.
+	 *
+	 * @ticket 65652
+	 *
+	 * @dataProvider data_wp_json_encode
+	 *
+	 * @param mixed  $data     Data to encode.
+	 * @param string $expected Expected JSON string.
+	 */
+	public function test_wp_json_encode( $data, $expected ) {
+		$this->assertSame( $expected, wp_json_encode( $data ) );
+	}
+
+	/**
+	 * Data provider for test_wp_json_encode().
+	 *
+	 * @return array<string, array{
+	 *     data:     mixed,
+	 *     expected: string,
+	 * }>
+	 */
+	public function data_wp_json_encode(): array {
+		return array(
+			'simple array'  => array(
+				array(
+					'a' => 1,
+					'b' => 2
+				),
+				'{"a":1,"b":2}',
+			),
+			'nested object' => array(
+				(object) array( 'a' => array( 1, 2 ) ),
+				'{"a":[1,2]}',
+			),
+			'string'        => array(
+				'hello world',
+				'"hello world"',
+			),
+			'integer'       => array(
+				123,
+				'123',
+			),
+		);
+	}
+
+	/**
+	 * Tests encoding with options.
+	 *
+	 * @ticket 65652
+	 */
+	public function test_wp_json_encode_options() {
+		$data = array( 'a' => 1 );
+		$this->assertSame( "{\n    \"a\": 1\n}", wp_json_encode( $data, JSON_PRETTY_PRINT ) );
+	}
+
+	/**
+	 * Tests encoding with depth.
+	 *
+	 * @ticket 65652
+	 */
+	public function test_wp_json_encode_depth() {
+		$data = array( 'a' => array( 'b' => 1 ) );
+		// Depth 1 should fail to encode the nested array.
+		$this->assertFalse( wp_json_encode( $data, 0, 1 ) );
+		// Depth 2 should succeed.
+		$this->assertSame( '{"a":{"b":1}}', wp_json_encode( $data, 0, 2 ) );
+	}
+
+	/**
+	 * Tests handling of invalid UTF-8.
+	 *
+	 * wp_json_encode() attempts to fix invalid UTF-8 by using _wp_json_prepare_data().
+	 *
+	 * @ticket 65652
+	 */
+	public function test_wp_json_encode_invalid_utf8() {
+		// Invalid UTF-8 sequence.
+		$invalid_utf8 = "Invalid\x80UTF8";
+		$encoded      = wp_json_encode( $invalid_utf8 );
+
+		// It should not be false, it should have attempted to fix it.
+		$this->assertNotFalse( $encoded );
+		// In newer PHP versions, json_encode might handle it or it's sanitized to 'Invalid' or similar.
+		// WordPress's _wp_json_sanity_check will attempt to clean it.
+		$this->assertStringContainsString( 'Invalid', $encoded );
+	}
+}