algorithms-and-data-structures/AlgorithmsAndDataStructures.Tests/DataStructures/BinarySearchTrees/BinarySearchTreeTests.cs at master · arst/algorithms-and-data-structures · GitHub

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using System;
using AlgorithmsAndDataStructures.DataStructures.BinarySearchTrees;
using AlgorithmsAndDataStructures.DataStructures.Common;
using Xunit;

namespace AlgorithmsAndDataStructures.Tests.DataStructures.BinarySearchTrees;

public class BinarySearchTreeTests
{
    [Fact]
    public void EmptyTreeCorrectlyReportsItsEmptiness()
    {
        var sut = new BinarySearchTree<int>();
        Assert.True(sut.IsEmpty());
    }

    [Fact]
    public void NonEmptyTreeCorrectlyReportsItsEmptiness()
    {
        var sut = new BinarySearchTree<int>();
        sut.Insert(1);
        Assert.False(sut.IsEmpty());
    }


    [Fact]
    public void InsertToAnEmptyTreeCreatesRoot()
    {
        var sut = new BinarySearchTree<int>();

        sut.Insert(1);

        var dfsInOrder = sut.DepthFirstTraversalInOrder();

        Assert.Equal(1, dfsInOrder[0]);
    }

    [Fact]
    public void LeftSubtreeIsBinarySearchTree()
    {
        var sut = new BinarySearchTree<int>();

        sut.Insert(4);
        sut.Insert(2);
        sut.Insert(3);
        sut.Insert(1);

        var root = sut.GetRoot();

        Assert.Equal(4, root.Value);
        Assert.Equal(2, root.Left.Value);
        Assert.Equal(1, root.Left.Left.Value);
        Assert.Equal(3, root.Left.Right.Value);
    }

    [Fact]
    public void RightSubtreeIsBinarySearchTree()
    {
        var sut = new BinarySearchTree<int>();

        sut.Insert(1);
        sut.Insert(3);
        sut.Insert(2);
        sut.Insert(4);

        var root = sut.GetRoot();

        Assert.Equal(1, root.Value);
        Assert.Equal(3, root.Right.Value);
        Assert.Equal(2, root.Right.Left.Value);
        Assert.Equal(4, root.Right.Right.Value);
    }

    [Fact]
    public void AllSubtreesAreBinarySearchTrees()
    {
        var sut = new BinarySearchTree<int>();
        var random = new Random();

        for (var j = 0; j < 10; j++)
        for (var i = 0; i < 100000; i++)
        {
            var number = random.Next();
            sut.Insert(number);
        }

        CheckInvariantRecursive(sut.GetRoot());
    }

    [Fact]
    public void AllSubtreesAreBinarySearchTreesAfterDeletes()
    {
        var sut = new BinarySearchTree<int>();
        var random = new Random();

        for (var j = 0; j < 100; j++)
        {
            for (var i = 0; i < 10000; i++)
            {
                var number = random.Next(1000);
                sut.Insert(number);
            }

            for (var z = 0; z < 1000; z++)
            {
                var number = random.Next(1000);
                sut.Delete(number);

                CheckInvariantRecursive(sut.GetRoot());
            }
        }
    }

    private void CheckInvariantRecursive(BinaryTreeNode<int> root)
    {
        if (root.Left != null)
        {
            Assert.True(root.Value > root.Left.Value);
            CheckInvariantRecursive(root.Left);
        }

        if (root.Right != null)
        {
            Assert.True(root.Value < root.Right.Value);
            CheckInvariantRecursive(root.Right);
        }
    }
}