SwiftUI StandardPreviews - reusable previews with dark- and light-mode, large- and small-text (Dynamic Type) variations.

StandardPreviews.swift

import SwiftUI

struct StandardPreviews<Content: View> : View {
    
    var light: Bool = true
    var dark: Bool = true
    var large: Bool = true
    var small: Bool = true
    
    var content: () -> Content
    
    var body: some View {
        Group {
            
            if light {
                content()
                    .environment(\.colorScheme, .light)
            }
            
            if dark {
                content()
                    .environment(\.colorScheme, .dark)
            }
            
            if large {
                content()
                    .environment(\.sizeCategory, .accessibilityExtraLarge)
            }
            
            if small {
                content()
                    .environment(\.sizeCategory, .extraSmall)
            }
        }
    }
}

struct StandardPreviews_Previews : PreviewProvider {
    static var previews: some View {
        StandardPreviews {
            NavigationView {
                Text("Hello")
            }
        }
    }
}