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..e918774b4 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 +45,8 @@ public double getSalary() {
   public void setSalary(double salary) {
     this.salary = salary;
   }
+
+  public String getDetails() {
+    return "ID: " + id + ", Name: " + name + ", Department: " + department + ", Salary: " + salary;
+  }
 }
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..fb82e98f4
--- /dev/null
+++ b/lesson_15/tdd/tdd_app/src/test/java/com/codedifferently/lesson15/EmployeeManagerTest.java
@@ -0,0 +1,87 @@
+package com.codedifferently.lesson15;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+import org.junit.jupiter.api.Test;
+
+public class EmployeeManagerTest {
+  @Test
+  void testAddEmployee() {
+    // Arrange
+    EmployeeManager manager = new EmployeeManager();
+    Employee employee = new Employee(1, "Jane Doe", "Marketing", 65000.00);
+
+    // Act
+    manager.addEmployee(employee);
+    Employee retrievedEmployee = manager.getEmployee(1);
+
+    // Assert
+    assertThat(retrievedEmployee).isNotNull();
+    assertThat(retrievedEmployee.getName()).isEqualTo("Jane Doe");
+  }
+
+  @Test
+  void testUpdateEmployee() {
+    // Arrange
+    EmployeeManager manager = new EmployeeManager();
+    Employee employee = new Employee(1, "John Doe", "Engineering", 75000.00);
+    manager.addEmployee(employee);
+
+    // Act
+    employee.setName("John Smith");
+    manager.updateEmployee(employee);
+    Employee updatedEmployee = manager.getEmployee(1);
+
+    // Assert
+    assertThat(updatedEmployee.getName()).isEqualTo("John Smith");
+  }
+
+  @Test
+  void testEmployeeCount() {
+    // Arrange
+    EmployeeManager manager = new EmployeeManager();
+    manager.addEmployee(new Employee(1, "John Doe", "Engineering", 75000.00));
+    manager.addEmployee(new Employee(2, "Jane Doe", "Marketing", 65000.00));
+
+    // Act
+    int count = manager.getEmployeeCount();
+
+    // Assert
+    assertThat(count).isEqualTo(2);
+  }
+
+  @Test
+  void testRemoveEmployeeThrowsExceptionWhenNotFound() {
+    // Arrange
+    EmployeeManager manager = new EmployeeManager();
+
+    // Act & Assert
+    assertThatThrownBy(() -> manager.removeEmployee(99))
+        .isInstanceOf(IllegalArgumentException.class)
+        .hasMessageContaining("Employee does not in collection with id 99");
+  }
+
+  @Test
+  void testGetEmployeeThrowsExceptionWhenNotFound() {
+    // Arrange
+    EmployeeManager manager = new EmployeeManager();
+
+    // Act & Assert
+    assertThatThrownBy(() -> manager.getEmployee(99))
+        .isInstanceOf(IllegalArgumentException.class)
+        .hasMessageContaining("Employee does not in collection with id 99");
+  }
+
+  @Test
+  void testUpdateEmployeeThrowsExceptionWhenNotFound() {
+    // Arrange
+    EmployeeManager manager = new EmployeeManager();
+    Employee employee = new Employee(1, "John Doe", "Engineering", 75000.00);
+
+    // Act & Assert
+    assertThatThrownBy(() -> manager.updateEmployee(employee))
+        .isInstanceOf(IllegalArgumentException.class)
+        .hasMessageContaining("Employee does not in collection with id 1");
+  }
+}
diff --git a/lesson_15/tdd/tdd_app/src/test/java/com/codedifferently/lesson15/EmployeeTest.java b/lesson_15/tdd/tdd_app/src/test/java/com/codedifferently/lesson15/EmployeeTest.java
new file mode 100644
index 000000000..488f26b94
--- /dev/null
+++ b/lesson_15/tdd/tdd_app/src/test/java/com/codedifferently/lesson15/EmployeeTest.java
@@ -0,0 +1,50 @@
+package com.codedifferently.lesson15;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+public class EmployeeTest {
+  @Test
+  void testEmployeeCreationAndDetails() {
+    // Arrange
+    Employee employee = new Employee(1, "John Doe", "Engineering", 75000.00);
+
+    // Act
+    String details = employee.getDetails();
+
+    // Assert
+    assertThat(details)
+        .isEqualTo("ID: 1, Name: John Doe, Department: Engineering, Salary: 75000.0");
+  }
+
+  @Test
+  void testGetters() {
+    // Arrange
+    Employee employee = new Employee(1, "John Doe", "Engineering", 75000.00);
+
+    // Act & Assert
+    assertThat(employee.getId()).isEqualTo(1);
+    assertThat(employee.getName()).isEqualTo("John Doe");
+    assertThat(employee.getDepartment()).isEqualTo("Engineering");
+    assertThat(employee.getSalary()).isEqualTo(75000.00);
+  }
+
+  @Test
+  void testSetters() {
+    // Arrange
+    Employee employee = new Employee(1, "John Doe", "Engineering", 75000.00);
+
+    // Act
+    employee.setId(2);
+    employee.setName("Jane Doe");
+    employee.setDepartment("Marketing");
+    employee.setSalary(65000.00);
+
+    // Assert
+    assertThat(employee.getId()).isEqualTo(2);
+    assertThat(employee.getName()).isEqualTo("Jane Doe");
+    assertThat(employee.getDepartment()).isEqualTo("Marketing");
+    assertThat(employee.getSalary()).isEqualTo(65000.00);
+  }
+}