Don't improperly cast IDs when fetching post, user, or term objects.

Blindly casting passed IDs to integers can generate false positives
when the ID is cast to `1`.

Props deeptiboddapati.
Fixes #37738.

git-svn-id: https://develop.svn.wordpress.org/trunk@38381 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/post/wpPost.php

@@ -0,0 +1,100 @@
+<?php
+
+/**
+ * @group post
+ */
+class Tests_Post_WpPost extends WP_UnitTestCase {
+	protected static $post_id;
+
+	public static function wpSetUpBeforeClass( $factory ) {
+		global $wpdb;
+
+		// Ensure that there is a post with ID 1.
+		if ( ! get_post( 1 ) ) {
+			$wpdb->insert( $wpdb->posts, array(
+				'ID' => 1,
+				'post_title' => 'Post 1',
+			) );
+		}
+
+		self::$post_id = self::factory()->post->create();
+	}
+
+	public static function wpTearDownAfterClass() {
+		wp_delete_post( 1, true );
+		wp_delete_post( self::$post_id, true );
+	}
+
+	/**
+	 * @ticket 37738
+	 */
+	public function test_get_instance_should_work_for_numeric_string() {
+		$found = WP_Post::get_instance( (string) self::$post_id );
+
+		$this->assertSame( self::$post_id, $found->ID );
+	}
+
+	/**
+	 * @ticket 37738
+	 */
+	public function test_get_instance_should_fail_for_negative_number() {
+		$found = WP_Post::get_instance( -self::$post_id );
+
+		$this->assertFalse( $found );
+	}
+
+	/**
+	 * @ticket 37738
+	 */
+	public function test_get_instance_should_fail_for_non_numeric_string() {
+		$found = WP_Post::get_instance( 'abc' );
+
+		$this->assertFalse( $found );
+	}
+
+	/**
+	 * @ticket 37738
+	 */
+	public function test_get_instance_should_fail_for_bool() {
+		$found = WP_Post::get_instance( true );
+
+		$this->assertFalse( $found );
+	}
+
+	/**
+	 * @ticket 37738
+	 */
+	public function test_get_instance_should_succeed_for_float_that_is_equal_to_post_id() {
+		$found = WP_Post::get_instance( 1.0 );
+
+		$this->assertSame( 1, $found->ID );
+	}
+
+	/**
+	 * @ticket 37738
+	 */
+	public function test_get_instance_should_fail_for_float() {
+		$found = WP_Post::get_instance( 1.6 );
+
+		$this->assertFalse( $found );
+	}
+
+	/**
+	 * @ticket 37738
+	 */
+	public function test_get_instance_should_fail_for_array() {
+		$found = WP_Post::get_instance( array( 1 ) );
+
+		$this->assertFalse( $found );
+	}
+
+	/**
+	 * @ticket 37738
+	 */
+	public function test_get_instance_should_fail_for_class() {
+		$class = new stdClass();
+		$found = WP_Post::get_instance( $class );
+
+		$this->assertFalse( $found );
+	}
+}