add some test case

Author: ngtduc693

Algorithms.Tests/Algorithms.Tests.csproj

@@ -20,6 +20,7 @@
     </PackageReference>
     <PackageReference Include="FluentAssertions" Version="6.12.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
+    <PackageReference Include="Moq" Version="4.20.72" />
     <PackageReference Include="nunit" Version="4.0.1" />
     <PackageReference Include="NUnit3TestAdapter" Version="4.5.0" />
   </ItemGroup>

Algorithms.Tests/RecommenderSystem/CollaborativeFilteringTests.cs

@@ -1,4 +1,5 @@
 using Algorithms.RecommenderSystem;
+using Moq;
 using NUnit.Framework;
 using System.Collections.Generic;
 
@@ -7,13 +8,15 @@ namespace Algorithms.Tests.RecommenderSystem
     [TestFixture]
     public class CollaborativeFilteringTests
     {
-        private CollaborativeFiltering recommender = new();
+        private Mock<ISimilarityCalculator>? mockSimilarityCalculator;
+        private CollaborativeFiltering? recommender;
         private Dictionary<string, Dictionary<string, double>> testRatings = null!;
 
         [SetUp]
         public void Setup()
         {
-            recommender = new CollaborativeFiltering();
+            mockSimilarityCalculator = new Mock<ISimilarityCalculator>();
+            recommender = new CollaborativeFiltering(mockSimilarityCalculator.Object);
 
             testRatings = new Dictionary<string, Dictionary<string, double>>
             {
@@ -49,7 +52,7 @@ public void CalculateSimilarity_WithValidInputs_ReturnsExpectedResults(
             var user1Ratings = new Dictionary<string, double> { [commonItem] = rating1 };
             var user2Ratings = new Dictionary<string, double> { [commonItem] = rating2 };
 
-            var similarity = recommender.CalculateSimilarity(user1Ratings, user2Ratings);
+            var similarity = recommender?.CalculateSimilarity(user1Ratings, user2Ratings);
 
             Assert.That(similarity, Is.InRange(-1.0, 1.0));
         }
@@ -60,17 +63,33 @@ public void CalculateSimilarity_WithNoCommonItems_ReturnsZero()
             var user1Ratings = new Dictionary<string, double> { ["item1"] = 5.0 };
             var user2Ratings = new Dictionary<string, double> { ["item2"] = 4.0 };
 
-            var similarity = recommender.CalculateSimilarity(user1Ratings, user2Ratings);
+            var similarity = recommender?.CalculateSimilarity(user1Ratings, user2Ratings);
 
             Assert.That(similarity, Is.EqualTo(0));
         }
 
         [Test]
         public void PredictRating_WithNonexistentItem_ReturnsZero()
         {
-            var predictedRating = recommender.PredictRating("nonexistentItem", "user1", testRatings);
+            var predictedRating = recommender?.PredictRating("nonexistentItem", "user1", testRatings);
 
             Assert.That(predictedRating, Is.EqualTo(0));
         }
+
+        [Test]
+        public void PredictRating_WithOtherUserHavingRatedTargetItem_ShouldCalculateSimilarityAndWeightedSum()
+        {
+            var targetItem = "item1";
+            var targetUser = "user1";
+
+            mockSimilarityCalculator?
+                .Setup(s => s.CalculateSimilarity(It.IsAny<Dictionary<string, double>>(), It.IsAny<Dictionary<string, double>>()))
+                .Returns(0.8);
+
+            var predictedRating = recommender?.PredictRating(targetItem, targetUser, testRatings);
+
+            Assert.That(predictedRating, Is.Not.EqualTo(0.0d));
+            Assert.That(predictedRating, Is.EqualTo(3.5d).Within(0.01));
+        }
     }
 }

Algorithms/RecommenderSystem/CollaborativeFiltering.cs

@@ -6,6 +6,13 @@ namespace Algorithms.RecommenderSystem
 {
     public class CollaborativeFiltering
     {
+        private readonly ISimilarityCalculator similarityCalculator;
+
+        public CollaborativeFiltering(ISimilarityCalculator similarityCalculator)
+        {
+            this.similarityCalculator = similarityCalculator;
+        }
+
         /// <summary>
         /// Method to calculate similarity between two users using Pearson correlation.
         /// </summary>
@@ -70,7 +77,7 @@ public double PredictRating(string targetItem, string targetUser, Dictionary<str
                 var otherUserRatings = ratings[otherUser];
                 if (otherUserRatings.ContainsKey(targetItem))
                 {
-                    var similarity = CalculateSimilarity(targetUserRatings, otherUserRatings);
+                    var similarity = similarityCalculator.CalculateSimilarity(targetUserRatings, otherUserRatings);
                     totalSimilarity += Math.Abs(similarity);
                     weightedSum += similarity * otherUserRatings[targetItem];
                 }

Algorithms/RecommenderSystem/ISimilarityCalculator.cs

@@ -0,0 +1,13 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Algorithms.RecommenderSystem
+{
+    public interface ISimilarityCalculator
+    {
+        double CalculateSimilarity(Dictionary<string, double> user1Ratings, Dictionary<string, double> user2Ratings);
+    }
+}