Unit 1.2: Error, Fault, Failure & Incident

Understanding the difference between these terms is crucial in software engineering.

1. Definitions & Chain of Events

1. Error (Mistake):

• A human action that produces an incorrect result.
• Example: A programmer forgets a semicolon or misunderstands a formula.

2. Fault (Defect/Bug):

• A manifestation of an error in the software. It is the incorrect code or logic.
• Example: The line of code average = a + b / 2 instead of average = (a + b) / 2.

3. Failure:

• Deviation of the specific module from its expected service. It occurs when the faulty code is executed.
• Example: The program outputs "4.5" instead of "5.0".

4. Incident:

• When a failure is observed and reported. It is the symptom visible to the user.

The Chain:

Person makes an Error → Creates a Fault in code → Execution leads to Failure → Reported as an Incident.

2. Taxonomies (Classifying Faults)

Software faults can be classified into different categories to help understand their root cause.

3. Test Cases

A Test Case is a set of conditions under which a tester determines whether a system is working as originally established or not.

Components of a Test Case:

• Test Case ID: Unique identifier.
• Test Description: What are we testing?
• Pre-conditions: What must be true before starting (e.g., "User is logged in").
• Test Steps: Step-by-step actions.
• Test Data: Inputs (e.g., Username: "admin", Password: "123").
• Expected Result: What should happen.
• Actual Result: What actually happened.
• Status: Pass/Fail.