Unit 2.1: Black Box Testing & Techniques

1. Functional Testing (Black Box Testing)

Definition: Black Box Testing (also known as Functional Testing) is a testing method where the internal structure/design/implementation of the item being tested is not known to the tester. The tester interacts with the system solely through the interface (GUI, API inputs).

Why "Black Box"? Imagine a literal black box where you cannot see inside. You put an input (X) into a slot, and you get an output (Y) from another slot. You verify if Y is correct for X, without caring how the box produced Y.

Characteristics:

• Requires: Requirements and Functional Specifications.
• Performed by: Independent Testers (QA) or End Users.
• Focus: Functionality, UX, External behavior.

Advantages:

• Tester doesn't need to know coding.
• Testing is done from the user's perspective.
• Helps expose missing functionality or interface errors.

Disadvantages:

• Cannot test hidden logic or complex paths inside the code.
• Redundant test cases might be written if the tester doesn't know how code works.

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2. Boundary Value Analysis (BVA)

Definition: A technique based on the idea that "errors aggregate at boundaries". Programmers often make "Off-by-one" errors (e.g., using < instead of <=).

Concept: Instead of testing the middle values, we focus on the edges.

Rules for Range [Min, Max]:

1. Valid Min: (The minimum value allowed).
2. Valid Max: (The maximum value allowed).
3. Invalid Min-1: (Just below the minimum).
4. Invalid Max+1: (Just above the maximum).

Detailed Example:

• Requirement: An "Age" field accepts values from 18 to 60.
• Test Case 1 (Min): Enter 18 -> Accept.
• Test Case 2 (Max): Enter 60 -> Accept.
• Test Case 3 (Min-1): Enter 17 -> Error Message.
• Test Case 4 (Max+1): Enter 61 -> Error Message.
• Note: Software often breaks at 17 or 61 due to boundary conditions.

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3. Equivalence Class Partitioning (ECP)

Definition: A technique where input data is divided into logical groups called Equivalence Classes. Data elements within one class are expected to be processed in the same way by the software.

Concept: Testing one value from a class is as good as testing all values from that class. This dramatically reduces the number of test cases.

Types of Classes:

1. Valid Class: Set of inputs that should be accepted.
2. Invalid Class: Set of inputs that should be rejected.

Detailed Example:

• Requirement: An application accepts a "Zip Code" which must be a 5-digit number.
• Partition 1 (Valid): Any 5-digit number (e.g., 10000 to 99999). Test Data: 12345.
• Partition 2 (Invalid - Length): Less than 5 digits. Test Data: 123.
• Partition 3 (Invalid - Length): More than 5 digits. Test Data: 123456.
• Partition 4 (Invalid - Type): Non-numeric characters. Test Data: ABCDE.

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4. Decision Table Based Testing

Definition: A "Cause-Effect" table used to test systems with complex rules, where the output depends on a combination of inputs. It is excellent for logic verification.

Components:

1. Conditions (Process inputs): Questions with Yes/No answers.
2. Actions (Process outputs): What the system should do.
3. Rules: Columns showing the combination of conditions.

Detailed Example: E-Commerce Discount Logic Rules:

• "New Users get 10% off."
• "Orders over $100 get Free Shipping."
• "Premium Members always get Free Shipping."

Decision Table:

Benefit: It ensures no combination of rules is missed.