Introduce unit testing on calculation objects

Tests/Builders/BuilderExtensions.cs

@@ -0,0 +1,80 @@
+using Core.Entities;
+
+namespace Tests.Builders;
+
+/// <summary>
+/// Helper utilities for working with test data builders.
+/// </summary>
+public static class BuilderExtensions
+{
+    /// <summary>
+    /// Resets all builder ID counters to 1.
+    /// Call this in test SetUp to ensure test isolation.
+    /// </summary>
+    public static void ResetAllBuilders()
+    {
+        EventDefinitionBuilder.ResetIdCounter();
+        StudentBuilder.ResetIdCounter();
+        TeamBuilder.ResetIdCounter();
+    }
+
+    /// <summary>
+    /// Creates a student with event rankings for multiple events.
+    /// </summary>
+    /// <param name="builder">The student builder</param>
+    /// <param name="rankedEvents">Dictionary of events to their ranks (1-10)</param>
+    /// <returns>The builder for method chaining</returns>
+    public static StudentBuilder WithRankings(this StudentBuilder builder, Dictionary<EventDefinition, int> rankedEvents)
+    {
+        foreach (var (eventDef, rank) in rankedEvents)
+        {
+            builder.WithRanking(eventDef, rank);
+        }
+        return builder;
+    }
+
+    /// <summary>
+    /// Creates a team with a captain as the first student.
+    /// </summary>
+    /// <param name="builder">The team builder</param>
+    /// <param name="students">Students to add (first one becomes captain)</param>
+    /// <returns>The builder for method chaining</returns>
+    public static TeamBuilder WithStudentsAndCaptain(this TeamBuilder builder, params Student[] students)
+    {
+        if (students.Length == 0)
+            return builder;
+
+        builder.WithStudents(students);
+        builder.WithCaptain(students[0]);
+        return builder;
+    }
+
+    /// <summary>
+    /// Creates multiple event definitions at once.
+    /// </summary>
+    /// <param name="names">Event names</param>
+    /// <returns>Array of individual event definitions</returns>
+    public static EventDefinition[] CreateIndividualEvents(params string[] names)
+    {
+        return names.Select(name => EventDefinitionBuilder.Individual(name).Build()).ToArray();
+    }
+
+    /// <summary>
+    /// Creates multiple students at once with sequential names.
+    /// </summary>
+    /// <param name="count">Number of students to create</param>
+    /// <param name="baseFirstName">Base first name (will be suffixed with numbers)</param>
+    /// <param name="baseLastName">Base last name</param>
+    /// <returns>Array of students</returns>
+    public static Student[] CreateStudents(int count, string baseFirstName = "Student", string baseLastName = "Test")
+    {
+        var students = new Student[count];
+        for (int i = 0; i < count; i++)
+        {
+            students[i] = StudentBuilder.Default()
+                .WithName($"{baseFirstName}{i + 1}", baseLastName)
+                .Build();
+        }
+        return students;
+    }
+}