Fix custom taxonomy query structure in build_query_args method

The tax_query argument for WP_Query requires an array of arrays, not a flat array.
Added unit test to verify proper structure for custom taxonomy queries.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: wpscholar

RandomPostOnRefresh.php

@@ -280,8 +280,11 @@ public static function build_query_args( $atts ) {
 					$query_args['tag__in'] = $terms;
 				} else {
 					$query_args['tax_query'] = array(
-						'taxonomy' => $atts['taxonomy'],
-						'terms'    => $terms,
+						array(
+							'taxonomy' => $atts['taxonomy'],
+							'field'    => 'term_id',
+							'terms'    => $terms,
+						),
 					);
 				}
 			}
@@ -371,4 +374,4 @@ public static function error( $message, $example = '' ) {
 
 	add_action( 'plugins_loaded', array( 'RandomPostOnRefresh', 'initialize' ) );
 
-}
+}

tests/RandomPostOnRefreshTest.php

@@ -134,6 +134,27 @@ public function test_build_query_args_with_taxonomy() {
 		$args = RandomPostOnRefresh::build_query_args( $atts );
 		$this->assertEquals( array( 3, 4 ), $args['category__in'] );
 	}
+	
+	/**
+	 * Test build_query_args with custom taxonomy and terms.
+	 */
+	public function test_build_query_args_with_custom_taxonomy() {
+		$atts = array_merge(
+			RandomPostOnRefresh::DEFAULT_ATTRIBUTES,
+			array(
+				'post_type' => 'post',
+				'taxonomy'  => 'custom_tax',
+				'terms'     => '5,6',
+			)
+		);
+		$args = RandomPostOnRefresh::build_query_args( $atts );
+		$this->assertArrayHasKey( 'tax_query', $args );
+		$this->assertIsArray( $args['tax_query'] );
+		$this->assertIsArray( $args['tax_query'][0] );
+		$this->assertEquals( 'custom_tax', $args['tax_query'][0]['taxonomy'] );
+		$this->assertEquals( 'term_id', $args['tax_query'][0]['field'] );
+		$this->assertEquals( array( 5, 6 ), $args['tax_query'][0]['terms'] );
+	}
 
 	/**
 	 * Test build_query_args with show=image and image_required=true.