test: cover msls_get_switcher() argument handling

Add an isolated test for includes/api.php covering the no-arg
call, an explicit attribute array, and coercion of a non-array
value (the '' the [sc_msls] shortcode passes). Runs in a separate
process so loading api.php does not collide with the Brain Monkey
function stubs used elsewhere in the suite.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: apermo

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( '' ) );
+	}
+}