Add unit test

tests/php/features/TestFacet.php

@@ -442,6 +442,34 @@ public function test_get_settings_schema() {
 		);
 	}
 
+	/**
+	 * Test ep_facet_selected_filters filter.
+	 *
+	 * @since 5.2.0
+	 * @group facets
+	 */
+	public function test_ep_facet_selected_filters() {
+		$facet_feature = Features::factory()->get_registered_feature( 'facets' );
+
+		parse_str( 'ep_filter_taxonomy=dolor,sit', $_GET );
+
+		$add_prefix_with_term = function( $filter ) {
+			$new_terms = [];
+			foreach ( $filter['taxonomies']['taxonomy']['terms'] as $key => $value ) {
+				$new_terms[ 'cap-' . $key ] = $value;
+			}
+
+			$filter['taxonomies']['taxonomy']['terms'] = $new_terms;
+			return $filter;
+		};
+		add_filter( 'ep_facet_selected_filters', $add_prefix_with_term );
+
+		$selected = $facet_feature->get_selected();
+		foreach ( $selected['taxonomies']['taxonomy']['terms'] as $key => $value ) {
+			$this->assertStringStartsWith( 'cap-', $key );
+		}
+	}
+
 	/**
 	 * Utilitary function for the testGetSelected test.
 	 *