Add a test to validate the bug is fixed

tests/phpunit/includes/SummaryGeneratorTest.php

@@ -0,0 +1,42 @@
+<?php
+/**
+ * Tests for the Summary_Generator.
+ *
+ * @package Accessibility_Checker
+ */
+
+use EDAC\Inc\Summary_Generator;
+
+/**
+ * Testing that the summary generator outputs what is expected when invoked.
+ */
+class SummaryGeneratorTest extends WP_UnitTestCase {
+	/**
+	 * Validates that a bug was fixed where the summary density would cause
+	 * a fatal error when the density_data had a string instead of an array.
+	 *
+	 * @throws ReflectionException If the method does not exist this is thrown.
+	 */
+	public function test_summary_density_wont_error_when_density_array_does_not_have_array_inside() {
+		$post_id = self::factory()->post->create();
+		update_post_meta( $post_id, '_edac_density_data', '0,0' );
+
+		$simplified_summary = new Summary_Generator( $post_id );
+
+		// Reflection means that the method was hard to test in isolation and
+		// likely warrants a refactor so that the method is more testable.
+		$method = ( new ReflectionClass( get_class( $simplified_summary ) ) )
+			->getMethod( 'update_issue_density' );
+		$method->setAccessible( true );
+
+		$method->invoke( $simplified_summary, array() );
+
+		// We are really testing here that the method does not throw an error,
+		// but we may as well check that the meta didn't change as well since
+		// we are here and by this point already know the method did not fatal.
+		$this->assertEquals(
+			'0,0',
+			get_post_meta( $post_id, '_edac_density_data', true )
+		);
+	}
+}