diff --git a/includes/api.php b/includes/api.php
index b230259b..0a6b312f 100644
--- a/includes/api.php
+++ b/includes/api.php
@@ -10,10 +10,11 @@
  * Get the output for using the links to the translations in your code
  *
  * @package Msls
- * @param mixed $attr
+ * @since 3.0.0 The $attr parameter is optional and defaults to an empty array.
+ * @param mixed $attr Optional. Attributes forwarded to the switcher output. Default empty array.
  * @return string
  */
-function msls_get_switcher( $attr ): string {
+function msls_get_switcher( $attr = array() ): string {
 	$arr = is_array( $attr ) ? $attr : array();
 	$obj = apply_filters( 'msls_get_output', null );
 
diff --git a/tests/phpunit/TestApi.php b/tests/phpunit/TestApi.php
new file mode 100644
index 00000000..44d4cf39
--- /dev/null
+++ b/tests/phpunit/TestApi.php
@@ -0,0 +1,45 @@
+<?php declare( strict_types=1 );
+
+namespace lloc\MslsTests;
+
+use Brain\Monkey\Functions;
+use PHPUnit\Framework\Attributes\PreserveGlobalState;
+use PHPUnit\Framework\Attributes\RunTestsInSeparateProcesses;
+
+#[RunTestsInSeparateProcesses]
+#[PreserveGlobalState( false )]
+final class TestApi extends MslsUnitTestCase {
+
+	protected function setUp(): void {
+		parent::setUp();
+
+		require_once __DIR__ . '/../../includes/api.php';
+	}
+
+	public function test_msls_get_switcher_without_arguments(): void {
+		Functions\expect( 'apply_filters' )->once()->with( 'msls_get_output', null )->andReturn( null );
+
+		$this->assertSame( '', msls_get_switcher() );
+	}
+
+	public function test_msls_get_switcher_with_array(): void {
+		$attr = array( 'before_item' => '<li>' );
+
+		$output = \Mockery::mock();
+		$output->shouldReceive( 'set_tags' )->once()->with( $attr )->andReturn( 'switcher' );
+
+		Functions\expect( 'apply_filters' )->once()->with( 'msls_get_output', null )->andReturn( $output );
+
+		$this->assertSame( 'switcher', msls_get_switcher( $attr ) );
+	}
+
+	public function test_msls_get_switcher_coerces_non_array_to_empty_array(): void {
+		$output = \Mockery::mock();
+		$output->shouldReceive( 'set_tags' )->once()->with( array() )->andReturn( 'switcher' );
+
+		Functions\expect( 'apply_filters' )->once()->with( 'msls_get_output', null )->andReturn( $output );
+
+		// The [sc_msls] shortcode passes '' when used without attributes.
+		$this->assertSame( 'switcher', msls_get_switcher( '' ) );
+	}
+}