write

import std.array : appender;
import std.string : outdent, stripLeft;

auto output = appender!string;
const dependencies = [Dependency("a", "b")];

output.write(dependencies);

const expected = `
    @startuml
    package a {}
    package b {}

    a ..> b
    @enduml
    `;

assert(output.data == outdent(expected).stripLeft, output.data);