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..05ef794d9 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 + "\nName: " + name + "\nDepartment: " + department + "\nSalary: " + 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..d2991b22a
--- /dev/null
+++ b/lesson_15/tdd/tdd_app/src/test/java/com/codedifferently/lesson15/EmployeeManagerTest.java
@@ -0,0 +1,72 @@
+package com.codedifferently.lesson15;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+import java.util.HashMap;
+import java.util.Map;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+class EmployeeManagerTest {
+  EmployeeManager employeeManager;
+  private Map<Integer, Employee> employees;
+
+  @BeforeEach
+  void setUp() {
+    employees = new HashMap<>();
+    employees.put(1, new Employee(1, "John", "Marketing", 20000.50));
+    employees.put(2, new Employee(2, "Jane", "Accounting", 30000.70));
+    employeeManager = new EmployeeManager();
+    for (Map.Entry<Integer, Employee> entry : employees.entrySet()) {
+      employeeManager.addEmployee(entry.getValue());
+    }
+  }
+
+  @Test
+  public void testGetEmployee() {
+    // Arange
+    var id = 1;
+
+    // Act
+    Employee result = employeeManager.getEmployee(id);
+
+    // Assert
+    assertThat(result).isNotNull();
+    assertThat(result.getName()).isEqualTo("John");
+  }
+
+  @Test
+  public void testUpdateEmployee() {
+    // Arrange
+    var id = 2;
+
+    // Act
+    Employee employee = employeeManager.getEmployee(id); // use this for set test
+    employee.setDepartment("Human Resources");
+    employeeManager.updateEmployee(employee);
+    Employee updatedEmployee = employeeManager.getEmployee(id);
+
+    // Assert
+    assertThat(updatedEmployee).isNotNull();
+  }
+
+  @Test
+  public void testGetEmployeeCount() {
+    // Assert
+    assertThat(employeeManager.getEmployeeCount()).isNotNull();
+  }
+
+  @Test
+  public void testRemoveEmployee() {
+    var id = 1;
+
+    int count = employeeManager.getEmployeeCount();
+    employeeManager.removeEmployee(id);
+
+    assertThatThrownBy(() -> employeeManager.getEmployee(id))
+        .isInstanceOf(IllegalArgumentException.class)
+        .hasMessage("Employee does not in collection with id " + id);
+    assertThat(employeeManager.getEmployeeCount()).isLessThan(count);
+  }
+}
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..18879b875
--- /dev/null
+++ b/lesson_15/tdd/tdd_app/src/test/java/com/codedifferently/lesson15/EmployeeTest.java
@@ -0,0 +1,63 @@
+package com.codedifferently.lesson15;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.HashMap;
+import java.util.Map;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+class EmployeeTest {
+  EmployeeManager employeeManager;
+  private Map<Integer, Employee> employees;
+
+  @BeforeEach
+  void setUp() {
+    employees = new HashMap<>();
+    employees.put(1, new Employee(1, "John", "Marketing", 20000.50));
+    employees.put(2, new Employee(2, "Jane", "Accounting", 30000.70));
+    employeeManager = new EmployeeManager();
+    for (Map.Entry<Integer, Employee> entry : employees.entrySet()) {
+      employeeManager.addEmployee(entry.getValue());
+    }
+  }
+
+  @Test
+  public void testGetSalary() {
+    // Arrange
+    var id = 1;
+
+    // Act
+    Employee employee = employeeManager.getEmployee(id);
+
+    // Assert
+    assertThat(employee.getSalary()).isNotNull();
+  }
+
+  @Test
+  public void testGetDepartment() {
+    // Arrange
+    var id = 1;
+
+    // Act
+    Employee employee = employeeManager.getEmployee(id);
+
+    // Assert
+    assertThat(employee.getDepartment()).isNotNull();
+  }
+
+  @Test
+  public void testGetDetails() {
+    // Arrange
+    var id = 1;
+
+    // Act
+    Employee employee = employeeManager.getEmployee(id);
+
+    // Assert
+    assertThat(employee.getDetails()).isNotNull();
+    assertThat(employee.getName()).isEqualTo("John");
+    assertThat(employee.getDepartment()).isEqualTo("Marketing");
+    assertThat(employee.getSalary()).isEqualTo(20000.50);
+  }
+}