Testing levels (unit, integration, system, acceptance) in Software Engineering - Step-by-Step Execution

Concept Flow - Testing levels (unit, integration, system, acceptance)

Start Testing

↓

Unit Testing

↓

Integration Testing

↓

System Testing

↓

Acceptance Testing

↓

End

Testing starts with small parts (unit), then checks combined parts (integration), then the whole system, and finally if it meets user needs (acceptance).

Execution Sample

Software Engineering

Test Levels:
1. Unit: Test small parts
2. Integration: Test combined parts
3. System: Test whole system
4. Acceptance: Test user needs

This shows the four main testing levels from smallest to largest scope.

Analysis Table

Step	Testing Level	What is tested?	Purpose	Example
1	Unit Testing	Individual functions or methods	Check if each small part works alone	Test if a function adds two numbers correctly
2	Integration Testing	Groups of combined units	Check if parts work together	Test if login function works with database access
3	System Testing	Complete system	Check if whole system meets requirements	Test if website works on different browsers
4	Acceptance Testing	System from user perspective	Check if system meets user needs and is ready	User tests if app does what they want

💡 All testing levels completed to ensure software quality and readiness

State Tracker

Testing Level	Start	After Step 1	After Step 2	After Step 3	Final
Unit Testing	Not done	Done	Done	Done	Done
Integration Testing	Not done	Not done	Done	Done	Done
System Testing	Not done	Not done	Not done	Done	Done
Acceptance Testing	Not done	Not done	Not done	Not done	Done

Key Insights - 3 Insights

Why do we test small parts first before testing the whole system?

Testing small parts first (unit testing) helps find problems early and makes fixing easier, as shown in step 1 of the execution_table.

What is the difference between system testing and acceptance testing?

System testing checks if the whole system works correctly (step 3), while acceptance testing checks if it meets user needs and is ready to use (step 4).

Can acceptance testing be done before system testing?

No, acceptance testing happens last after system testing ensures the system works, as shown in the flow and execution_table steps.

Visual Quiz - 3 Questions

Look at the execution_table, at which step do we test if parts work together?

A Step 2 - Integration Testing

B Step 1 - Unit Testing

C Step 3 - System Testing

D Step 4 - Acceptance Testing

💡 Hint

Check the 'What is tested?' column in execution_table row 2

According to variable_tracker, which testing level is completed last?

A Integration Testing

B Acceptance Testing

C System Testing

D Unit Testing

💡 Hint

Look at the 'Final' column in variable_tracker for each testing level

If a bug is found in a single function, which testing level should catch it first?

A Acceptance Testing

B System Testing

C Unit Testing

D Integration Testing

💡 Hint

Refer to execution_table step 1 about what unit testing covers

Concept Snapshot

Testing levels:
1. Unit: Test small parts alone
2. Integration: Test combined parts
3. System: Test whole system
4. Acceptance: Test if system meets user needs
Each level builds on the previous to ensure quality.

Full Transcript

Testing software happens in four main levels. First, unit testing checks small parts like functions to make sure they work alone. Next, integration testing checks if these parts work together properly. Then, system testing checks the entire system to see if it meets all requirements. Finally, acceptance testing checks if the system meets user needs and is ready to use. This order helps find problems early and ensures the software is reliable and useful before release.

Practice

1. Which testing level focuses on verifying the smallest parts of software, like individual functions or methods?

easy

A. Acceptance testing

B. Integration testing

C. System testing

D. Unit testing

Solution

1. Step 1: Understand the scope of unit testing

   Unit testing checks the smallest parts of software, such as individual functions or methods, to ensure they work correctly on their own.

2. Step 2: Compare with other testing levels

   Integration testing checks combined parts, system testing checks the whole system, and acceptance testing checks if the software meets user needs.

3. Final Answer:

   Unit testing -> Option D

4. Quick Check:

   Smallest parts tested = Unit testing [OK]

Hint: Smallest parts tested? Think unit tests first. [OK]

Common Mistakes:

• Confusing unit testing with integration testing
• Thinking system testing tests small parts
• Mixing acceptance testing with unit testing

2. Which of the following is the correct order of testing levels from smallest scope to largest scope?

easy

A. Unit, Integration, System, Acceptance

B. System, Unit, Acceptance, Integration

C. Acceptance, System, Integration, Unit

D. Integration, Unit, Acceptance, System

Solution

1. Step 1: Identify the scope of each testing level

   Unit tests check smallest parts, integration tests check combined parts, system tests check the whole system, and acceptance tests check user satisfaction.

2. Step 2: Arrange from smallest to largest scope

   The correct order is Unit, Integration, System, Acceptance.

3. Final Answer:

   Unit, Integration, System, Acceptance -> Option A

4. Quick Check:

   Smallest to largest = Unit -> Integration -> System -> Acceptance [OK]

Hint: Remember: Unit first, then Integration, System, Acceptance last. [OK]

Common Mistakes:

• Mixing up acceptance and system testing order
• Reversing unit and integration testing
• Assuming acceptance testing is first

3. Consider a software project where a developer writes tests to check if two modules work correctly together. Which testing level is this?

medium

A. Unit testing

B. System testing

C. Integration testing

D. Acceptance testing

Solution

1. Step 1: Understand the scenario of testing two modules together

   Testing if two modules work correctly together means checking their interaction, which is the focus of integration testing.

2. Step 2: Differentiate from other testing levels

   Unit testing checks single modules alone, system testing checks the entire software, and acceptance testing checks user requirements.

3. Final Answer:

   Integration testing -> Option C

4. Quick Check:

   Testing combined parts = Integration testing [OK]

Hint: Testing combined modules? Think integration testing. [OK]

Common Mistakes:

• Confusing unit testing with integration testing
• Thinking system testing means module pairs
• Assuming acceptance testing covers module interaction

4. A tester runs tests that check if the entire software system meets the specified requirements but notices some tests fail due to missing user feedback. What testing level is likely missing or incomplete?

medium

A. Integration testing

B. Acceptance testing

C. System testing

D. Unit testing

Solution

1. Step 1: Analyze the problem context

   The tests check if the whole system meets requirements but fail due to missing user feedback, indicating user acceptance is not confirmed.

2. Step 2: Identify the testing level related to user satisfaction

   Acceptance testing confirms if the software meets user needs and expectations, so missing this causes the issue.

3. Final Answer:

   Acceptance testing -> Option B

4. Quick Check:

   User feedback missing = Acceptance testing incomplete [OK]

Hint: Missing user feedback? Check acceptance testing. [OK]

Common Mistakes:

• Confusing system testing with acceptance testing
• Assuming unit testing covers user needs
• Ignoring the role of acceptance tests

5. A company wants to ensure their new app works correctly at every level before release. They start by testing individual functions, then test how modules work together, next test the full app, and finally get users to approve it. Which sequence of testing levels are they following?

hard

A. Unit, Integration, System, Acceptance

B. Integration, Unit, Acceptance, System

C. Acceptance, System, Integration, Unit

D. System, Unit, Acceptance, Integration

Solution

1. Step 1: Match each testing step to its level

   Testing individual functions is Unit testing; testing modules together is Integration testing; testing the full app is System testing; user approval is Acceptance testing.

2. Step 2: Arrange the sequence in correct order

   The sequence is Unit, Integration, System, Acceptance.

3. Final Answer:

   Unit, Integration, System, Acceptance -> Option A

4. Quick Check:

   Stepwise testing = Unit -> Integration -> System -> Acceptance [OK]

Hint: Follow smallest to largest testing: Unit -> Integration -> System -> Acceptance. [OK]

Common Mistakes:

• Mixing order of testing levels
• Confusing acceptance with system testing
• Skipping integration testing step