Black-box testing techniques in Software Engineering - Step-by-Step Execution

Concept Flow - Black-box testing techniques

Start Testing

↓

Identify Inputs

↓

Apply Test Cases

↓

Observe Outputs

↓

Compare with Expected Results

↓

Pass

↓

Report

↓

End Testing

Black-box testing starts by identifying inputs, applying test cases, observing outputs, and comparing them to expected results to decide pass or fail.

Execution Sample

Software Engineering

Test Case: Input=5
Expected Output=10
Run Function with Input=5
Observe Output=10
Compare Output with Expected

This example tests if the function returns 10 when given input 5, without knowing internal code.

Analysis Table

Step	Action	Input	Observed Output	Expected Output	Result	Next Step
1	Apply test case	5		10	Pending	Run function
2	Run function	5	10	10	Pending	Compare outputs
3	Compare outputs	5	10	10	Pass	Report result
4	Report result	5	10	10	Pass	End testing

💡 Test ends after output matches expected result, confirming pass.

State Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
Input	None	5	5	5	5
Observed Output	None	None	10	10	10
Expected Output	None	10	10	10	10
Result	None	Pending	Pending	Pass	Pass

Key Insights - 2 Insights

Why don't we need to know the internal code to test?

Because black-box testing focuses only on inputs and outputs, as shown in execution_table steps 1-3, ignoring internal details.

What happens if the observed output does not match expected?

The test result would be 'Fail' and debugging starts, unlike the 'Pass' shown in step 3 of execution_table.

Visual Quiz - 3 Questions

Look at the execution_table at Step 2, what is the observed output?

A 10

B 5

C None

D Pending

💡 Hint

Check the 'Observed Output' column in execution_table row for Step 2.

At which step does the test result become 'Pass'?

A Step 1

B Step 4

C Step 3

D Step 2

💡 Hint

Look at the 'Result' column in execution_table to find when it changes to 'Pass'.

If the observed output was 8 instead of 10 at Step 2, what would be the result at Step 3?

A Pending

B Fail

C Pass

D Error

💡 Hint

Compare observed and expected outputs in execution_table to determine pass or fail.

Concept Snapshot

Black-box testing checks software by giving inputs and checking outputs.
It ignores internal code details.
Test steps: input → run → observe output → compare → pass/fail.
Used to find if software meets requirements.
Focus on what software does, not how it does it.

Full Transcript

Black-box testing techniques involve testing software by focusing only on inputs and outputs without looking at internal code. The process starts by identifying inputs, applying test cases, running the software, observing outputs, and comparing them with expected results. If outputs match, the test passes; otherwise, it fails and requires debugging. This method helps verify if the software behaves as expected from the user's perspective.

Practice

1. Which of the following best describes black-box testing?

easy

A. Testing software based on its functionality without looking at the code

B. Testing software by examining its internal code structure

C. Testing only the user interface of the software

D. Testing software performance under heavy load

Solution

1. Step 1: Understand black-box testing definition

   Black-box testing focuses on checking software behavior from the user's perspective without knowledge of internal code.

2. Step 2: Compare options with definition

   Testing software based on its functionality without looking at the code matches this definition exactly, while others describe different testing types.

3. Final Answer:

   Testing software based on its functionality without looking at the code -> Option A

4. Quick Check:

   Black-box testing = Functionality testing without code [OK]

Hint: Black-box tests check outputs, not code details [OK]

Common Mistakes:

• Confusing black-box with white-box testing
• Thinking black-box tests only UI
• Assuming black-box tests check performance

2. Which of these is a common technique used in black-box testing?

easy

A. Equivalence partitioning

B. Code coverage analysis

C. Static code review

D. Memory leak detection

Solution

1. Step 1: Identify black-box testing techniques

   Equivalence partitioning divides input data into groups to reduce test cases, a classic black-box method.

2. Step 2: Eliminate non-black-box options

   Code coverage and static code review require code knowledge; memory leak detection is performance testing.

3. Final Answer:

   Equivalence partitioning -> Option A

4. Quick Check:

   Black-box technique = Equivalence partitioning [OK]

Hint: Black-box uses input grouping like equivalence partitioning [OK]

Common Mistakes:

• Choosing code-based techniques for black-box
• Confusing static analysis with black-box testing
• Mixing performance tools with black-box

3. Consider a function that accepts an integer input from 1 to 100. Using boundary value analysis, which of the following is a valid boundary value?

medium

A. 0

B. 50

C. 1

D. 101

Solution

1. Step 1: Understand boundary value analysis

   This technique tests values at the edges of input ranges, such as minimum and maximum valid inputs.

2. Step 2: Identify valid boundary values

   Valid input range is 1 to 100, so boundaries are 1 and 100. Among options, 1 is a boundary value.

3. Final Answer:

   1 -> Option C

4. Quick Check:

   Boundary value = 1 [OK]

Hint: Test inputs at range edges, not middle or invalid [OK]

Common Mistakes:

• Choosing invalid inputs like 0 or 101 as boundaries
• Picking middle values instead of edges
• Confusing equivalence partitioning with boundary testing

4. A tester wrote these test cases for a login form: empty username, empty password, valid username and password, invalid username. What is missing for good black-box testing?

medium

A. Testing with SQL injection strings

B. Testing with boundary values for input length

C. Reviewing the source code for errors

D. Checking server logs for errors

Solution

1. Step 1: Analyze given test cases

   Tests cover empty and valid/invalid inputs but do not check input length boundaries.

2. Step 2: Identify missing black-box technique

   Boundary value analysis for input length is important to catch edge errors, missing here.

3. Final Answer:

   Testing with boundary values for input length -> Option B

4. Quick Check:

   Missing boundary tests = Testing with boundary values for input length [OK]

Hint: Check input length edges for thorough black-box tests [OK]

Common Mistakes:

• Confusing security tests with black-box functional tests
• Thinking code review is part of black-box testing
• Ignoring boundary value analysis

5. You have a form that accepts age between 18 and 60. Using black-box testing, which set of inputs covers equivalence partitioning and boundary value analysis?

hard

A. 18, 19, 59, 60

B. 18, 30, 60

C. 0, 18, 60, 100

D. 17, 18, 30, 60, 61

Solution

1. Step 1: Understand equivalence partitioning and boundary value analysis

   Equivalence partitioning divides inputs into valid and invalid groups; boundary value analysis tests edges of valid ranges.

2. Step 2: Check options for both techniques

   17, 18, 30, 60, 61 includes invalid low (17), valid boundaries (18, 60), valid middle (30), and invalid high (61), covering partitions and boundaries.

3. Final Answer:

   17, 18, 30, 60, 61 -> Option D

4. Quick Check:

   Both partitions and boundaries = 17, 18, 30, 60, 61 [OK]

Hint: Include invalid, boundary, and normal inputs for full coverage [OK]

Common Mistakes:

• Ignoring invalid inputs in test sets
• Testing only valid inputs without boundaries
• Confusing boundary values with just middle values