Why Boundary value analysis in Testing Fundamentals? - Purpose & Use Cases

The Big Idea

What if testing just a few smart numbers could catch most bugs hidden in your app?

The Scenario

Imagine you have to check a form where users enter their age between 18 and 60. You try every number one by one, from 18 to 60, to see if the form accepts it.

The Problem

Testing every single number is slow and boring. You might miss important numbers near the edges, like 17 or 61, which can cause bugs. It's easy to make mistakes and waste time.

The Solution

Boundary value analysis helps by focusing tests on the edges of the allowed range, like 17, 18, 19 and 59, 60, 61. This way, you catch most errors quickly without testing every number.

Before vs After

✗ Before

test_age(18); test_age(19); test_age(20); ... test_age(60);

✓ After

test_age(17); test_age(18); test_age(19); test_age(59); test_age(60); test_age(61);

What It Enables

It makes testing faster and smarter by catching bugs where they usually happen -- at the boundaries.

Real Life Example

When a bank app asks for a deposit amount between $100 and $10,000, boundary value analysis tests $99, $100, $101 and $9,999, $10,000, $10,001 to ensure correct behavior.

Key Takeaways

Manual testing every input is slow and error-prone.

Boundary value analysis targets edge cases where bugs often hide.

This method saves time and improves test quality.

Practice

1. What is the main goal of Boundary Value Analysis in software testing?

easy

A. To test the software's user interface design

B. To test inputs at the edges of input ranges

C. To test the software's performance under load

D. To test only the middle values of input ranges

Solution

1. Step 1: Understand boundary value analysis purpose

   Boundary value analysis focuses on testing the edges or limits of input ranges where errors often occur.

2. Step 2: Compare options with definition

   Only To test inputs at the edges of input ranges correctly describes testing inputs at the edges of input ranges.

3. Final Answer:

   To test inputs at the edges of input ranges -> Option B

4. Quick Check:

   Boundary value analysis = test edges [OK]

Hint: Focus on testing minimum and maximum input values [OK]

Common Mistakes:

• Confusing boundary testing with performance testing
• Testing only middle values instead of edges
• Ignoring values just outside the boundaries

2. Which of the following is the correct set of test inputs for boundary value analysis of an input field that accepts values from 1 to 10?

easy

A. 1, 5, 10

B. 0, 5, 10

C. 2, 5, 9

D. 0, 1, 10, 11

Solution

1. Step 1: Identify boundary values for range 1 to 10

   Boundaries are minimum (1) and maximum (10). Values just outside are 0 and 11.

2. Step 2: Check options for boundary and just outside values

   0, 1, 10, 11 includes 0 (just below min), 1 (min), 10 (max), and 11 (just above max), which is correct for boundary testing.

3. Final Answer:

   0, 1, 10, 11 -> Option D

4. Quick Check:

   Include min, max, and just outside values [OK]

Hint: Always test min, max, and values just outside boundaries [OK]

Common Mistakes:

• Testing only valid values inside the range
• Ignoring values just outside the boundaries
• Choosing random values without boundary focus

3. Consider a function that accepts an integer input from 5 to 15 inclusive. Which of the following test inputs is NOT a valid boundary value test case?

medium

A. 10

B. 5

C. 4

D. 15

Solution

1. Step 1: Identify boundary values and just outside values

   Boundaries are 5 (min) and 15 (max). Just outside are 4 and 16.

2. Step 2: Check which input is not a boundary or just outside value

   Inputs 4, 5, and 15 are boundary or just outside values. 10 is a normal middle value, not a boundary test case.

3. Final Answer:

   10 -> Option A

4. Quick Check:

   Boundary tests exclude middle values like 10 [OK]

Hint: Exclude middle values; test edges and just outside only [OK]

Common Mistakes:

• Including middle values as boundary tests
• Ignoring values just outside boundaries
• Confusing valid inputs with boundary inputs

4. A tester wrote these boundary test inputs for a field accepting values 10 to 20: 9, 10, 20, 21. The test failed for input 21. What is the most likely reason?

medium

A. The software has a bug accepting 21

B. The test inputs are incorrect; 21 should be accepted

C. 21 is outside the valid input range and should fail

D. Boundary value analysis does not require testing outside the range

Solution

1. Step 1: Understand boundary test inputs and expected behavior

   Inputs 9 and 21 are just outside the valid range 10 to 20, so failure on 21 is expected.

2. Step 2: Analyze test failure reason

   Since 21 is invalid input, failure means software correctly rejects it. So test failure is expected, not a bug.

3. Final Answer:

   21 is outside the valid input range and should fail -> Option C

4. Quick Check:

   Outside boundary inputs should cause failure [OK]

Hint: Expect failure for inputs just outside boundaries [OK]

Common Mistakes:

• Thinking failure on invalid input is a bug
• Not testing values just outside boundaries
• Assuming all test inputs must pass

5. A form accepts age input from 18 to 60 inclusive. Using boundary value analysis, which set of test inputs covers all necessary boundary cases including just outside values?

hard

A. 17, 18, 60, 61

B. 18, 30, 60

C. 16, 18, 59, 61

D. 18, 19, 59, 60

Solution

1. Step 1: Identify boundary and just outside values for age 18 to 60

   Boundaries are 18 (min) and 60 (max). Just outside are 17 (below min) and 61 (above max).

2. Step 2: Check which option includes all boundaries and just outside values

   17, 18, 60, 61 includes 17, 18, 60, and 61, covering all required boundary and just outside values.

3. Final Answer:

   17, 18, 60, 61 -> Option A

4. Quick Check:

   Test min, max, and just outside values for full coverage [OK]

Hint: Always include min, max, and one value outside each boundary [OK]

Common Mistakes:

• Missing just outside boundary values
• Testing only valid inputs inside range
• Confusing boundary values with random inputs