How to write RestAssured test when we have some custom custom input param with FileUpload inside Rest endpoint

I have following POST endpoint inside my Quarkus project:

    @PUT
    @Consumes(MediaType.MULTIPART_FORM_DATA)
    @Path("{var}/some-def")
    public Response saveReportDefinition(
        @PathParam("var")
        String var,
        @NotNull
        @Valid
        FileUploadInput fileInput,
        @Context
        UriInfo uriInfo
    ) {
        return Response.ok().build();
    }

where my FileUploadInput looks lie this:

import org.jboss.resteasy.reactive.multipart.FileUpload;

public record FileUploadInput(
    @NotNull
    @RestForm("file1")
    FileUpload file1,
    @NotNull
    @RestForm("file2")
    FileUpload file2,
    @NotNull
    @RestForm("file3")
    FileUpload file3
) {} 

I have following test method with RestAssured framework:

@Test
@DisplayName("Test Upload")
public void testUpload() {

    // 1. Prepare test data
    File file1 = getResourceAsFile("/dir/file1.json");
    File file2 = getResourceAsFile("/dir/file2.txt");
    File file3 = getResourceAsFile("/dir/file3.sql");

    // 2. Construct the request

    Response response = given()
        .contentType(ContentType.MULTIPART)
        .multiPart(?????)
        .put(BASE_URL + "Commission/report-definition");


    // 3. Validate the response
    response.then()
            .statusCode(200) // Expecting a successful response (HTTP 200)
            .body(is(emptyOrNullString())); // Assuming empty or null response body

}

Now how to write proper test with restassured framework for such endpoint?

I have written following test according to @geoand (thanks for answer) instructions which failed

@Test
@DisplayName("Test Upload")
public void testUpload() {

    // 1. Prepare test data
    File file1 = getResourceAsFile("/dir/file1.json");
    File file2 = getResourceAsFile("/dir/file2.txt");
    File file3 = getResourceAsFile("/dir/file3.sql");

    // 2. Construct the request

    Response response = given()
        .contentType(ContentType.MULTIPART)
        .multiPart("metaFile", file1, MediaType.TEXT_PLAIN)
        .multiPart("jsonFile", file2, MediaType.APPLICATION_JSON)
        .multiPart("sqlFile", file3, MediaType.TEXT_PLAIN)
        .put(BASE_URL + "Commission/report-definition");


    // 3. Validate the response
    response.then()
            .statusCode(200) // Expecting a successful response (HTTP 200)
            .body(is(emptyOrNullString())); // Assuming empty or null response body

}

but if I implemented saveReportDefinition() without record like

    @PUT
    @Consumes(MediaType.MULTIPART_FORM_DATA)
    @Path("{var}/some-def")
    public Response saveReportDefinition(
        @PathParam("var")
        String var,
        @NotNull
        @RestForm("file1")
        FileUpload file1,
        @NotNull
        @RestForm("file2")
        FileUpload file2,
        @NotNull
        @RestForm("file3")
        FileUpload file3
        @Context
        UriInfo uriInfo
    ) {
        return Response.ok().build();
    }

then everything worked. Then I tried to model FileUploadInput as class and not like a record as before

import org.jboss.resteasy.reactive.multipart.FileUpload;

public class FileUploadInput {
    @NotNull
    @RestForm("file1")
    public FileUpload file1,
    @NotNull
    @RestForm("file2")
    public FileUpload file2,
    @NotNull
    @RestForm("file3")
    public FileUpload file3
} 

and then automagically test started working. I do not know why does the records do not work in testing. I am using Quarkus v. 3.8.4 with Java 17 Temurin.