Spring multipart file upload test with TestRestTemplate and ByteArrayResource

application.yml

spring.servlet.multipart.max-file-size: 300MB
spring.servlet.multipart.max-request-size: 300MB

build.gradle.kts

import org.gradle.api.tasks.testing.logging.TestLogEvent.*
import org.jetbrains.kotlin.gradle.tasks.KotlinCompile

plugins {
	id("org.springframework.boot") version "2.4.3"
	id("io.spring.dependency-management") version "1.0.11.RELEASE"
	kotlin("jvm") version "1.4.30"
	kotlin("plugin.spring") version "1.4.30"
}

group = "com.example"
version = "0.0.1-SNAPSHOT"

java {
	toolchain {
		languageVersion.set(JavaLanguageVersion.of(15))
	}
}

repositories {
	mavenCentral()
}

dependencies {
	implementation("org.springframework.boot:spring-boot-starter-web") {
		exclude(group = "org.springframework.boot", module = "spring-boot-starter-tomcat")
	}
	implementation("org.springframework.boot:spring-boot-starter-undertow")
	implementation("com.fasterxml.jackson.module:jackson-module-kotlin")
	implementation("org.jetbrains.kotlin:kotlin-reflect")
	implementation("org.jetbrains.kotlin:kotlin-stdlib-jdk8")
	testImplementation("org.springframework.boot:spring-boot-starter-test")
}

tasks.withType<KotlinCompile> {
	kotlinOptions {
		freeCompilerArgs = listOf("-Xjsr305=strict")
		jvmTarget = "15"
	}
}

tasks.withType<Test> {
	useJUnitPlatform()
	minHeapSize = "1g"
	maxHeapSize = "1g"
	testLogging {
		events = setOf(PASSED, FAILED, SKIPPED, STANDARD_OUT, STANDARD_ERROR)
	}
}

UploadTestApplication.kt

package com.example.uploadtest

import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication
import org.springframework.web.bind.annotation.PostMapping
import org.springframework.web.bind.annotation.RequestParam
import org.springframework.web.bind.annotation.RestController
import org.springframework.web.multipart.MultipartFile

@SpringBootApplication
class UploadTestApplication

fun main(args: Array<String>) {
	runApplication<UploadTestApplication>(*args)
}

@RestController
class ApiController {

	@PostMapping("/binary")
	fun binary(@RequestParam data: MultipartFile) {
		println(data)
	}

}

UploadTestApplicationTests.kt

package com.example.uploadtest

import org.junit.jupiter.api.Assertions
import org.junit.jupiter.api.Test
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.test.context.SpringBootTest
import org.springframework.boot.test.context.SpringBootTest.WebEnvironment.RANDOM_PORT
import org.springframework.boot.test.web.client.TestRestTemplate
import org.springframework.core.io.ByteArrayResource
import org.springframework.http.MediaType
import org.springframework.http.RequestEntity
import org.springframework.util.LinkedMultiValueMap
import org.springframework.util.unit.DataSize

@SpringBootTest(webEnvironment = RANDOM_PORT)
class UploadTestApplicationTests {

	companion object {
		val SIZE = DataSize.ofMegabytes(200).toBytes().toInt()
	}

	@Autowired
	lateinit var restTemplate: TestRestTemplate

	@Test
	fun maximumUploadSize() {
		val resource = object : ByteArrayResource(ByteArray(SIZE)) {
			override fun getFilename() = "data.txt"
		}
		val request = RequestEntity.post("/binary")
			.contentType(MediaType.MULTIPART_FORM_DATA)
			.body(LinkedMultiValueMap<String, Any>().apply { add("data", resource) })
		val response = restTemplate.exchange(request, String::class.java)
		Assertions.assertTrue(response.statusCode.is2xxSuccessful)
	}

}