diff --git a/lesson_15/tdd/tdd_app/src/main/java/com/codedifferently/lesson15/Employee.java b/lesson_15/tdd/tdd_app/src/main/java/com/codedifferently/lesson15/Employee.java
index 49aaabbd7..368139e7e 100644
--- a/lesson_15/tdd/tdd_app/src/main/java/com/codedifferently/lesson15/Employee.java
+++ b/lesson_15/tdd/tdd_app/src/main/java/com/codedifferently/lesson15/Employee.java
@@ -45,4 +45,24 @@ public double getSalary() {
   public void setSalary(double salary) {
     this.salary = salary;
   }
+
+  public boolean isEqualTo(int otherId) {
+    return this.id == otherId;
+  }
+
+  public String getDetails() {
+    return "id: "
+        + this.getId()
+        + " name: "
+        + this.getName()
+        + " department: "
+        + this.getDepartment()
+        + " salary: "
+        + this.getSalary();
+  }
+
+  public void put(Employee employee) {
+    // TODO Auto-generated method stub
+    throw new UnsupportedOperationException("Unimplemented method 'put'");
+  }
 }
diff --git a/lesson_15/tdd/tdd_app/src/main/java/com/codedifferently/lesson15/EmployeeManager.java b/lesson_15/tdd/tdd_app/src/main/java/com/codedifferently/lesson15/EmployeeManager.java
index 4ac9edc41..32c5a2ce0 100644
--- a/lesson_15/tdd/tdd_app/src/main/java/com/codedifferently/lesson15/EmployeeManager.java
+++ b/lesson_15/tdd/tdd_app/src/main/java/com/codedifferently/lesson15/EmployeeManager.java
@@ -5,39 +5,37 @@
 
 public class EmployeeManager {
 
-  private final Map<Integer, Employee> employees;
+  private Map<Integer, Employee> employees = new HashMap<>();
 
-  public EmployeeManager() {
-    employees = new HashMap<>();
+  public void addEmployee(Employee employee) {
+    employees.put(employee.getId(), employee);
   }
 
-  public void addEmployee(Employee employee) {
+  public void removeEmployee(int id) {
+    employees.remove(id);
+  }
+
+  public void updateEmployee(Employee employee) {
     employees.put(employee.getId(), employee);
   }
 
   public Employee getEmployee(int id) {
-    assertEmployeeInCollection(id);
     return employees.get(id);
   }
 
-  public void updateEmployee(Employee employee) {
-    assertEmployeeInCollection(employee.getId());
-    employees.put(employee.getId(), employee);
+  public int getEmployeeCount() {
+    return employees.size();
   }
 
-  public void removeEmployee(int id) {
-    assertEmployeeInCollection(id);
-    employees.remove(id);
+  public Map<Integer, Employee> getEmployees() {
+    return employees;
   }
 
-  private void assertEmployeeInCollection(int id) {
-    if (this.employees.containsKey(id)) {
-      return;
-    }
-    throw new IllegalArgumentException("Employee does not in collection with id " + id);
+  public void setEmployees(Map<Integer, Employee> employees) {
+    this.employees = employees;
   }
 
-  public int getEmployeeCount() {
-    return employees.size();
+  public EmployeeManager() {
+    employees = new HashMap<>();
   }
 }
diff --git a/lesson_15/tdd/tdd_app/src/test/java/com/codedifferently/lesson15/Employee.Test.java b/lesson_15/tdd/tdd_app/src/test/java/com/codedifferently/lesson15/Employee.Test.java
new file mode 100644
index 000000000..025d64ce1
--- /dev/null
+++ b/lesson_15/tdd/tdd_app/src/test/java/com/codedifferently/lesson15/Employee.Test.java
@@ -0,0 +1,80 @@
+package com.codedifferently.lesson15;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+class EmployeeTest {
+
+  Employee employee;
+
+  // Set up
+  @BeforeEach
+  void setUp() {
+    employee = new Employee(7, "Nile", "SWE", 65000.00);
+  }
+
+  @Test
+  public void testGetId() {
+    int actualId = employee.getId();
+    int expectedId = 7;
+    assertEquals(expectedId, actualId);
+  }
+
+  @Test
+  public void testSetID() {
+    int expectedSetId = 0;
+    employee.setId(expectedSetId);
+    assertEquals(expectedSetId, employee.getId());
+  }
+
+  @Test
+  public void testGetName() {
+    String expectedName = "Nile";
+    String actualName = employee.getName();
+    assertEquals(expectedName, actualName);
+  }
+
+  @Test
+  public void testSetName() {
+    String expectedSetName = "Nile";
+    employee.setName(expectedSetName);
+    assertEquals(expectedSetName, employee.getName());
+  }
+
+  @Test
+  public void testGetDepartment() {
+    String expectedDepartment = "SWE";
+    String actualDepartment = employee.getDepartment();
+    assertEquals(expectedDepartment, actualDepartment);
+  }
+
+  @Test
+  public void testSetDepartment() {
+    String expectedSetDepartment = "Tech";
+    employee.setDepartment(expectedSetDepartment);
+    assertEquals(expectedSetDepartment, employee.getDepartment());
+  }
+
+  @Test
+  public void testGetSalary() {
+    double expectedSalary = 65000.00;
+    double actualSalary = employee.getSalary();
+    assertEquals(expectedSalary, actualSalary);
+  }
+
+  @Test
+  public void testSetSalary() {
+    double expectedSetSalary = 100000.00;
+    employee.setSalary(expectedSetSalary);
+    assertEquals(expectedSetSalary, employee.getSalary());
+  }
+
+  @Test
+  public void testGetDetails() {
+    String actualDetails = employee.getDetails();
+    String expectedDetails = "id: 7 name: Nile department: SWE salary: 65000.0";
+    assertEquals(expectedDetails, actualDetails);
+  }
+}
diff --git a/lesson_15/tdd/tdd_app/src/test/java/com/codedifferently/lesson15/EmployeeManagerTest.java b/lesson_15/tdd/tdd_app/src/test/java/com/codedifferently/lesson15/EmployeeManagerTest.java
new file mode 100644
index 000000000..65344fb36
--- /dev/null
+++ b/lesson_15/tdd/tdd_app/src/test/java/com/codedifferently/lesson15/EmployeeManagerTest.java
@@ -0,0 +1,79 @@
+package com.codedifferently.lesson15;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.HashMap;
+import java.util.Map;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+public class EmployeeManagerTest {
+  private EmployeeManager employeeManager;
+  private Map<Integer, Employee> employees;
+  private Employee employee1;
+  private Employee employee2;
+
+  @BeforeEach
+  public void setup() {
+    employees = new HashMap<>();
+    employee1 = new Employee(1, "Nile", "SWE", 65000.00);
+    employee2 = new Employee(2, "Chino", "Marketing", 70000.00);
+
+    employeeManager = new EmployeeManager();
+    employeeManager.setEmployees(employees);
+    employeeManager.addEmployee(employee1);
+    employeeManager.addEmployee(employee2);
+  }
+
+  @Test
+  public void testEmployeeManagement() {}
+
+  @Test
+  public void addEmployee() {
+    assertThat(employees).hasSize(2);
+  }
+
+  @Test
+  public void getEmployee() {
+    Employee retrievedEmployee = employeeManager.getEmployee(2);
+    assertThat(retrievedEmployee.getName()).isEqualTo("Chino");
+  }
+
+  @Test
+  public void updateEmployee() {
+    employee1.setSalary(70000.00);
+    employeeManager.updateEmployee(employee1);
+
+    Employee updatedEmployee = employeeManager.getEmployee(1);
+    assertThat(updatedEmployee.getSalary()).isEqualTo(70000.00);
+  }
+
+  @Test
+  public void getEmployeeCount() {
+    int count = employeeManager.getEmployeeCount();
+    assertEquals(2, count);
+  }
+
+  @Test
+  public void getEmployees() {
+    Map<Integer, Employee> employeeMap = employeeManager.getEmployees();
+    assertThat(employeeMap.size()).isEqualTo(2);
+  }
+
+  @Test
+  public void setEmployees() {
+    Map<Integer, Employee> newEmployees = new HashMap<>();
+    newEmployees.put(3, new Employee(3, "Charlie", "HR", 75000.00));
+    employeeManager.setEmployees(newEmployees);
+
+    assertThat(employeeManager.getEmployees().size()).isEqualTo(1);
+  }
+
+  @Test
+  public void testGetDetails() {
+    String actualDetails = employee1.getDetails();
+    String expectedDetails = "id: 1 name: Nile department: SWE salary: 65000.0";
+    assertEquals(expectedDetails, actualDetails);
+  }
+}