Equivalence Partitioning in Software Testing

🔹 What is Equivalence Partitioning?

Equivalence Partitioning (EP) is a Black Box Testing technique where input values are divided into logical groups (partitions), and only one value from each group is tested. The assumption is that all values in a partition behave the same way, so testing one value represents the entire group.

📌 Example: If an input field accepts numbers from 1 to 100, we divide the input into three partitions:

• Invalid Partition (Below Range): ≤ 0
• Valid Partition: 1 – 100
• Invalid Partition (Above Range): ≥ 101
  Instead of testing all 100 valid values, we test one value from each partition (e.g., 0, 50, 101).

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🔹 Why Use Equivalence Partitioning?

✅ Reduces the Number of Test Cases → No need to test every possible input.
✅ Covers a Wide Range of Values → Ensures different cases are tested.
✅ Detects Input Validation Issues → Quickly finds incorrect handling of input.
✅ Useful for UI & Form Testing → Validates input fields efficiently.

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🔹 Example Scenarios for Equivalence Partitioning

📌 Example 1: Age Validation (Valid Range: 18 to 60)

Partition Type	Test Case Example	Expected Result
Invalid (Below 18)	17	❌ Error (Too Young)
Valid (Between 18-60)	30	✅ Accepted
Invalid (Above 60)	61	❌ Error (Too Old)

📌 Explanation: Instead of testing all ages, we test one value per partition:

• Invalid Partition (17) → Should be rejected
• Valid Partition (30) → Should be accepted
• Invalid Partition (61) → Should be rejected

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📌 Example 2: ATM Withdrawal (Valid Range: $100 – $5000, Multiples of $10 Only)

Partition Type	Test Case	Expected Outcome
Invalid (Below Min)	$50	❌ Error
Valid Range	$1000	✅ Approved
Invalid (Above Max)	$5500	❌ Error
Invalid (Not a Multiple of 10)	$125	❌ Error

📌 Explanation: We test only one value per partition instead of all possible amounts.

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📌 Example 3: Password Field (Min 8 – Max 20 Characters)

Partition Type	Test Case Example	Expected Result
Invalid (Too Short)	"abc123"	❌ Error
Valid (Correct Length)	"password1234"	✅ Accepted
Invalid (Too Long)	"thisisaverylongpassword123"	❌ Error

📌 Explanation: Instead of testing every possible password length, we test:

• Invalid Partition: "abc123" (Too short)
• Valid Partition: "password1234" (Accepted)
• Invalid Partition: "thisisaverylongpassword123" (Too long)

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🔹 Types of Equivalence Partitioning

1️⃣ Weak Equivalence Partitioning

• Divides input into broad categories (Valid/Invalid).
  📌 Example: If valid input is 1 – 100, test only one valid and one invalid value.

2️⃣ Strong Equivalence Partitioning

• Divides inputs into multiple partitions for detailed testing.
  📌 Example: A grading system (0-49 = Fail, 50-75 = Pass, 76-100 = Distinction).
  We test one value per grade: 25 (Fail), 60 (Pass), 85 (Distinction).

3️⃣ Boundary-Based Equivalence Partitioning

• Combines Equivalence Partitioning + Boundary Value Testing.
  📌 Example: A form allows ages 18 to 60 → Test 17, 18, 59, 60, 61 (minimum, maximum, and boundaries).

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🔹 Difference Between Equivalence Partitioning & Boundary Value Testing

Feature	Equivalence Partitioning (EP)	Boundary Value Testing (BVT)
Concept	Tests one value per range	Tests extreme min/max values
Number of Test Cases	Fewer	More (tests boundaries)
Focus	Ensures each partition behaves the same	Detects issues at limits
Example (Age 18-60)	Test one value (30)	Test 18, 60, and edges (17, 19, 59, 61)

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🔹 When to Use Equivalence Partitioning?

✔ When input has a defined range (e.g., age limits, salary range).
✔ When testing form fields (e.g., phone number, password length).
✔ When optimizing test cases (avoiding unnecessary repetitions).
✔ When testing numerical, date, or text-based inputs.