Replace count-based test assertions with explicit expected value lists

[jas88]

Problem

Many tests use count-based assertions like:

Assert.That(menu.Items, Has.Count.EqualTo(8));
Assert.That(results, Has.Count.EqualTo(3));

When these fail, the error message provides no diagnostic value:

Expected: 8
But was: 7

You have no idea what's missing or what changed.

Proposed Solution

Replace count assertions with explicit expected value comparisons:

// Before (poor diagnostics):
Assert.That(menu.Items, Has.Count.EqualTo(4));

// After (clear diagnostics):
var expected = new[] { "New", "Open", "Save", "Exit" };
Assert.That(menu.Items.Select(i => i.Text), Is.EqualTo(expected));

On failure, NUnit will show exactly which items differ:

Expected: ["New", "Open", "Save", "Exit"]
But was:  ["New", "Open", "Exit"]
Missing:  ["Save"]

Examples Found

• Rdmp.UI.Tests/ArbitraryFolderNodeTests.cs - menu item counts
• Rdmp.UI.Tests/AggregateEditorUITests.cs - dropdown item counts
• Rdmp.UI.Tests/HistoryProviderTests.cs - history counts
• Various tests using Has.Count.EqualTo(N) pattern

Guidelines

1. Order matters: Use Is.EqualTo(expected) when order is significant
2. Order doesn't matter: Use Is.EquivalentTo(expected) for set comparisons
3. Subset checks: Use Is.SupersetOf(expected) when only verifying certain items exist
4. Named values: Extract expected values to named constants/arrays for clarity

Exceptions

Some count assertions are appropriate:

• Row counts from database queries where content varies
• Verifying "at least N" with Is.GreaterThanOrEqualTo
• Performance tests measuring quantities

The goal is improving tests where the specific items are known and stable.