1.php

class Caldera_Forms_Files{
	//...
	public static function get_max_upload_size( array $field){}
	public static function is_file_too_large( array  $field, $path ){}
	//...
}

2.php

<?php
namespace calderawp\calderaforms\Tests\Integration;
use Caldera_Forms_Files;
use calderawp\calderaforms\Tests\Util\Traits\TestsImages;
class Caldera_Forms_FilesTest extends TestCase
{
	use TestsImages;
	protected $field = [
		'ID' => 'fld123',
		'type' => 'file',
		'config' => [
		],
	];
	/** @inheritdoc */
	public function tearDown()
	{
		$this->deleteTestCatFile();
		parent::tearDown();
	}
	
	//...
	
	/**
	 *
	 * @group now
	 *
	 * @since 1.8.0
	 *
	 * @covers Caldera_Forms_Files::get_max_upload_size()
	 */
	public function testGetMaxUploadSize()
	{
		$field = array_merge($this->field, [
			'config' => [ 'max_upload' => 42 ],
		]);
		//returns saved value
		$this->assertEquals( 42, Caldera_Forms_Files::get_max_upload_size($field ) );
		$field = array_merge($this->field, [
			'config' => [ 'max_upload' => '42' ],
		]);
		//always a string
		$this->assertEquals( 42, Caldera_Forms_Files::get_max_upload_size($field ) );
		//0 by default
		$this->assertEquals( 0, Caldera_Forms_Files::get_max_upload_size($this->field ) );
	}
	/**
	 *
	 * @group now
	 *
	 * @since 1.8.0
	 *
	 * @covers Caldera_Forms_Files::is_file_too_large()
	 * @covers Caldera_Forms_Files::get_max_upload_size()
	 */
	public function testIfFileIsTooLarge(){
		$field = array_merge($this->field, [
			'config' => [ 'max_upload' => 42 ],
		]);
		//This file is larger than 42 bytes
		$this->assertTrue(
			Caldera_Forms_Files::is_file_too_large($field, $this->getSmallCatPath() )
		);
		$field = array_merge($this->field, [
			'config' => [ 'max_upload' => 42000000 ],
		]);
		//This file is smaller than 42000000 bytes
		$this->assertFalse(
			Caldera_Forms_Files::is_file_too_large($field, $this->getSmallCatPath() )
		);
		//No limits, all files are the right size.
		$this->assertFalse(
			Caldera_Forms_Files::is_file_too_large($this->field, $this->getSmallCatPath() )
		);
	}
}

3.php

class Caldera_Forms_Files {
  //...
	/**
	 * Get max size for file field
	 *
	 * @since 1.8.0
	 *
	 * @param array $field Field config
	 *
	 * @return int
	 */
	public static function get_max_upload_size( array $field)
	{
		return ! empty( $field[ 'config']['max_upload'] ) ? absint( $field[ 'config']['max_upload']) : 0;
	}
	/**
	 * Check if a file is too large to upload
	 *
	 * @since 1.8.0
	 *
	 * Returns false if no max upload size set.
	 * Returns true if max upload size option is set and file is larger than limit
	 *
	 * @param array $field Field config
	 * @param string $path_to_file Path to check against
	 */
	public static function is_file_too_large( array  $field, $path_to_file )
	{
		return 0 !== self::get_max_upload_size($field) && self::get_max_upload_size($field) < filesize($path_to_file );
	}
 }

4.php

<?php
namespace calderawp\calderaforms\Tests\Integration\Handlers;
use calderawp\calderaforms\cf2\Exception;
use calderawp\calderaforms\cf2\Fields\Handlers\Cf1FileUploader;
use calderawp\calderaforms\cf2\Fields\Handlers\FileFieldHandler;
use calderawp\calderaforms\cf2\Fields\Handlers\FileUpload;
use calderawp\calderaforms\Tests\Integration\TestCase;
use calderawp\calderaforms\Tests\Util\Traits\TestsImages;
class FileFieldHandlerTest extends TestCase
{
	  use TestsImages;
    
	//...
	
	/**
	 * @since 1.8.0
	 *
	 * @cover \calderawp\calderaforms\cf2\Fields\Handlers\FileUpload::getAllowedTypes()
	 */
	public function testKnowsFileIsTooLarge()
	{
		$field = [ 'ID' => 'fld1', 'config' => [ 'max_upload' => 42 ] ];
		$form = [ 'ID' => 'cd1' ];
		$uploader = new Cf1FileUploader();
		$handler = new FileUpload($field, $form, $uploader);
		$this->assertTrue( $handler->isFileTooLarge($this->getSmallCatPath() ) );
	}
	/**
	 * @since 1.8.0
	 *
	 * @cover \calderawp\calderaforms\cf2\Fields\Handlers\FileUpload::processFiles()
	 * @cover \calderawp\calderaforms\cf2\Fields\Handlers\FileUpload::isFileTooLarge()
	 */
	public function testExceptionWhenFileIsTooLarge()
	{
		$this->expectException(Exception::class);
		$field = [ 'ID' => 'fld1', 'config' => [ 'max_upload' => 42 ] ];
		$form = [ 'ID' => 'cd1' ];
		$uploader = new Cf1FileUploader();
		$handler = new FileUpload($field, $form, $uploader);
		$handler->processFiles([ $this->getSmallCatPath() ], []);
	}
	/**
 	 *
	 * @since 1.8.0
	 *
	 * @cover \calderawp\calderaforms\cf2\Fields\Handlers\FileUpload::getAllowedTypes()
	 */
	public function testAllowsFileSize()
	{
		$field = [ 'ID' => 'fld1', 'config' => [ 'max_upload' => 0 ] ];
		$form = [ 'ID' => 'cd1' ];
		$uploader = new Cf1FileUploader();
		$handler = new FileUpload($field, $form, $uploader);
		$this->assertFalse( $handler->isFileTooLarge($this->getSmallCatPath() ) );
		$field = [ 'ID' => 'fld1', 'config' => [ 'max_upload' => 70000000 ] ];
		$form = [ 'ID' => 'cd1' ];
		$uploader = new Cf1FileUploader();
		$handler = new FileUpload($field, $form, $uploader);
		$this->assertFalse( $handler->isFileTooLarge($this->getSmallCatPath() ) );
	}
}