1. Make a new Contact object with invalid data, such as an empty string for the firstName field.
2. Attempt to initialize the object. Expected Result: The object initialization should fail and raise a ValueError with an appropriate error message.

Scenario 2 - Valid data validation Steps to test:

1. make a new Contact object with valid data.
2. Attempt to initialize the object. Expected Result: The object initialization should succeed, and the object should be initialized with the provided data.

Scenario 3 - toString method Steps to test:

1. make a new Contact object with valid data.
2. Call the toString method on the object. Expected Result: The toString method should return a string representation of the object's data.