xUnit Assert vs FluentAssertions vs Shouldly in C#, plus snapshot testing with Verify

// ======================================================================
// Q: xUnit Assert, FluentAssertions or Shouldly?
//
// - Fluent libraries give more readable failure messages. Caution:
//   FluentAssertions v8 moved to a paid license for commercial use. Many teams
//   stayed on v7 or switched to Shouldly / AwesomeAssertions.
// - Snapshot testing (Verify) for large outputs (JSON responses, generated SQL,
//   emails): the first run stores the result, later runs compare against it.
// ======================================================================

// xUnit
Assert.Equal(2, order.Lines.Count);
Assert.Collection(order.Lines,
    l => Assert.Equal("PIP-100", l.Sku),
    l => Assert.Equal("GLV-NIT-M", l.Sku));
Assert.Equivalent(new { Sku = "PIP-100", Quantity = 2 }, dto);    // structural comparison

// Shouldly
order.Status.ShouldBe(OrderStatus.Placed);
order.Lines.ShouldContain(l => l.Sku == "PIP-100");