The view for testing with _ViewTest.

View-SheeTestCase.swift

import SwiftUI
@testable import SheeKit
import XCTest

enum ID: String {
    case showPartDetailButton
    case changePartDetailButton
}

struct ShowPartDetail: View {
    var onDismiss: () -> Void
    @State var sheetDetail: InventoryItem?
    var body: some View {
        ZStack {
            HStack {
                Button("Show Part Details") {
                    sheetDetail = InventoryItem.first
                }
                .frame(maxWidth: .infinity)
                ._identified(by: ID.showPartDetailButton)
                Button("Change Part Details") {
                    if sheetDetail?.quantity ?? 0 < 100500 {
                        sheetDetail = InventoryItem.second
                    } else {
                        sheetDetail = nil
                    }
                }
                .frame(maxWidth: .infinity)
                ._identified(by: ID.changePartDetailButton)
            }
            .shee(item: $sheetDetail,
                  presentationStyle: presentationStyle,
                  onDismiss: onDismiss) { detail in
                VStack(alignment: .leading, spacing: 20) {
                    Text("Part Number: \(detail.partNumber)")
                    Text("Name: \(detail.name)")
                    Text("Quantity On-Hand: \(detail.quantity)")
                }
            }
        }
        .frame(maxWidth: .infinity, maxHeight: .infinity)
        .background(Color(.systemGreen.withAlphaComponent(0.2)))
    }
    
    var presentationStyle: ModalPresentationStyle {
        var sheetProperties = SheetProperties()
        sheetProperties.detents = sheetDetail?.quantity ?? 0 > 100500 ? [ .large() ] : [ .medium() ]
        return .formSheet(properties: sheetProperties)
    }
}

struct InventoryItem: Identifiable, Hashable {
    var id: String
    let partNumber: String
    let quantity: Int
    let name: String
    
    static let first = InventoryItem(
        id: "0123456789",
        partNumber: "Z-1234A",
        quantity: 100,
        name: "Widget")

    static let second = InventoryItem(
        id: "9876543210",
        partNumber: "A-4321Z",
        quantity: 100500,
        name: "Gadget")
}