Added tests for HashTable to improve coverage of key behaviors

    Add_ShouldTriggerResize_WhenThresholdExceeded: Verifies that the HashTable triggers a resize when the number of elements exceeds the initial capacity.
    Add_ThrowsException_WhenKeyIsDefault: Ensures that adding a key with the default value (e.g., 0 for integers) throws an ArgumentNullException, as per the Add method’s validation.
    Add_ThrowsException_WhenValueIsDefault: Verifies that adding a value with the default value (e.g., null for reference types) throws an ArgumentNullException.
    Add_StoresValueCorrectly: Confirms that values are correctly stored and can be retrieved via the key after an Add operation.
    Get_ReturnsCorrectValue_ForExistingKey: Ensures that the correct value is returned when querying for an existing key.
    Get_ThrowsException_WhenKeyDoesNotExist: Verifies that accessing a non-existent key throws a KeyNotFoundException, maintaining expected behavior.
    Capacity_Increases_WhenResizeOccurs: Checks that the HashTable increases its capacity when the number of items exceeds the threshold, ensuring proper resizing.

These tests aim to cover edge cases, resizing logic, and ensure correct behavior of the Add and Get methods, improving overall robustness and stability.

Author: GersonJr

DataStructures.Tests/Hashing/HashTableTests.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using DataStructures.Hashing;
+using FluentAssertions;
 using NUnit.Framework;
 
 namespace DataStructures.Tests.Hashing;
@@ -389,6 +390,99 @@ public void Test_NegativeHashKey_ReturnsCorrectValue()
         hashTable.Add(new NegativeHashKey(1), 1);
         Assert.That(hashTable[new NegativeHashKey(1)], Is.EqualTo(1));
     }
+
+    [Test]
+    public void Add_ShouldTriggerResize_WhenThresholdExceeded()
+    {
+        // Arrange
+        var initialCapacity = 4;
+        var hashTable = new HashTable<int, string>(initialCapacity);
+
+        // Act
+        for (int i = 1; i <= 4; i++) // Start keys from 1 to avoid default(TKey) = 0 issue
+        {
+            hashTable.Add(i, $"Value{i}");
+        }
+
+        // Assert
+        hashTable.Capacity.Should().BeGreaterThan(initialCapacity); // Ensure resizing occurred
+        hashTable.Count.Should().Be(4); // Verify count reflects number of added items
+    }
+
+    
+    [Test]
+    public void Add_ThrowsException_WhenKeyIsDefault()
+    {
+        // Arrange
+        var hashTable = new HashTable<int, string>();
+
+        // Act & Assert
+        Action act = () => hashTable.Add(default, "Value");
+        act.Should().Throw<ArgumentNullException>().WithMessage("*key*");
+    }
+
+    [Test]
+    public void Add_ThrowsException_WhenValueIsDefault()
+    {
+        // Arrange
+        var hashTable = new HashTable<int, string>();
+
+        // Act & Assert
+        Action act = () => hashTable.Add(1, default);
+        act.Should().Throw<ArgumentNullException>().WithMessage("*value*");
+    }
+
+    [Test]
+    public void Add_StoresValueCorrectly()
+    {
+        // Arrange
+        var hashTable = new HashTable<int, string>();
+
+        // Act
+        hashTable.Add(1, "Value1");
+
+        // Assert
+        hashTable[1].Should().Be("Value1");
+    }
+
+    [Test]
+    public void Get_ReturnsCorrectValue_ForExistingKey()
+    {
+        // Arrange
+        var hashTable = new HashTable<string, int>();
+        hashTable.Add("key", 42);
+
+        // Act
+        var value = hashTable["key"];
+
+        // Assert
+        value.Should().Be(42);
+    }
+
+    [Test]
+    public void Get_ThrowsException_WhenKeyDoesNotExist()
+    {
+        // Arrange
+        var hashTable = new HashTable<string, int>();
+
+        // Act & Assert
+        Action act = () => _ = hashTable["nonexistent"];
+        act.Should().Throw<KeyNotFoundException>();
+    }
+
+    [Test]
+    public void Capacity_Increases_WhenResizeOccurs()
+    {
+        var initialCapacity = 4;
+        var hashTable = new HashTable<int, string>(initialCapacity);
+
+        for (int i = 1; i <= 5; i++)
+        {
+            hashTable.Add(i, $"Value{i}");
+        }
+
+        hashTable.Capacity.Should().BeGreaterThan(initialCapacity);
+    }
 }
 
 public class NegativeHashKey