Why Statement coverage in Testing Fundamentals? - Purpose & Use Cases

The Big Idea

What if a tiny missed line in your code causes a big bug later?

The Scenario

Imagine you have a simple calculator app with many buttons and functions. You try each button one by one manually to see if it works. But you miss some buttons or forget to test some functions.

The Problem

Testing every part by hand is slow and tiring. You might skip some lines of code without knowing. This means bugs can hide and cause problems later.

The Solution

Statement coverage helps by checking if every single line of code runs at least once during tests. It shows exactly what parts you missed, so you can fix gaps and be sure your app works well.

Before vs After

✗ Before

Run app and click buttons randomly to check if they work.

✓ After

Use a statement coverage tool to see which lines ran during tests.

What It Enables

It makes sure no line of code is left untested, giving confidence that your software is reliable.

Real Life Example

A team testing a login feature uses statement coverage to confirm every step, like input checks and error messages, is tested before release.

Key Takeaways

Manual testing can miss code lines easily.

Statement coverage tracks which lines run during tests.

This helps find untested code and improve test quality.

Practice

1. What does statement coverage measure in software testing?

easy

A. The number of test cases written

B. The number of bugs found in the code

C. The time taken to run all tests

D. The percentage of code lines executed during testing

Solution

1. Step 1: Understand the definition of statement coverage

   Statement coverage measures how many lines of code are executed when tests run.

2. Step 2: Compare options to the definition

   Only The percentage of code lines executed during testing correctly describes statement coverage as the percentage of executed code lines.

3. Final Answer:

   The percentage of code lines executed during testing -> Option D

4. Quick Check:

   Statement coverage = executed code lines percentage [OK]

Hint: Statement coverage counts executed lines, not tests or bugs [OK]

Common Mistakes:

• Confusing statement coverage with number of test cases
• Thinking it measures bugs found
• Mixing it up with test execution time

2. Which of the following is the correct way to describe statement coverage in a test report?

easy

A. Statement coverage is the number of test cases executed.

B. Statement coverage is the percentage of code statements executed during testing.

C. Statement coverage is the total time taken to run all tests.

D. Statement coverage is the number of bugs found per test.

Solution

1. Step 1: Identify the correct definition for statement coverage in reports

   Statement coverage is reported as the percentage of code statements executed during tests.

2. Step 2: Match options to the correct definition

   Statement coverage is the percentage of code statements executed during testing. correctly states this; others confuse coverage with test count, time, or bugs.

3. Final Answer:

   Statement coverage is the percentage of code statements executed during testing. -> Option B

4. Quick Check:

   Statement coverage = % of executed statements [OK]

Hint: Coverage means percent of executed code lines, not test counts [OK]

Common Mistakes:

• Reporting coverage as number of tests
• Confusing coverage with test duration
• Mixing coverage with bug counts

3. Consider this code snippet:

if (x > 0) {
  print("Positive");
} else {
  print("Non-positive");
}

If a test runs with x = 5, what is the statement coverage?

medium

A. 100% because all lines run

B. 75% because some lines run

C. 50% because only the if block runs

D. 0% because no else block runs

Solution

1. Step 1: Count total statements in the code

   There are 4 statements: the if condition, print("Positive"), else, print("Non-positive").

2. Step 2: Identify executed statements when x=5

   The if condition and print("Positive") run; else and its print do not run. So 2 out of 4 statements run.

3. Final Answer:

   50% because only the if block runs -> Option C

4. Quick Check:

   Executed statements = 2/4 = 50% [OK]

Hint: Only executed lines count; else block skipped means less coverage [OK]

Common Mistakes:

• Assuming else block runs anyway
• Counting conditions as multiple statements
• Thinking coverage is always 100%

4. You have this code:

if (a == 10) {
  print("Ten");
}
print("Done");

A test runs with a = 5 but reports 100% statement coverage. What is wrong?

medium

A. The test did not execute the if block, so coverage cannot be 100%

B. The print("Done") statement was not executed

C. The test input is invalid

D. The coverage tool counts only executed lines, so 100% is correct

Solution

1. Step 1: Identify statements and their execution

   There are 3 statements: if condition, print("Ten"), and print("Done"). With a=5, the if block is skipped, so print("Ten") is not executed.

2. Step 2: Check coverage report validity

   Since one statement is not executed, coverage cannot be 100%. The report is incorrect or the test did not run as expected.

3. Final Answer:

   The test did not execute the if block, so coverage cannot be 100% -> Option A

4. Quick Check:

   Skipped statements mean coverage less than 100% [OK]

Hint: Skipped code means coverage less than 100%, check test inputs [OK]

Common Mistakes:

• Assuming coverage counts unexecuted lines
• Ignoring skipped if blocks
• Trusting coverage tool blindly

5. Given this code:

if (score >= 90) {
  grade = 'A';
} else if (score >= 80) {
  grade = 'B';
} else {
  grade = 'C';
}

Which test inputs will achieve 100% statement coverage?

hard

A. score = 95, score = 85, and score = 70

B. score = 95 and score = 85

C. score = 95 only

D. score = 70 only

Solution

1. Step 1: Identify all statements in the code

   There are 7 statements: 3 conditions and 4 assignments (grade = 'A', grade = 'B', grade = 'C', plus else blocks).

2. Step 2: Determine inputs to cover all branches

   To cover all statements, tests must run each branch: score=95 covers first if, score=85 covers else if, score=70 covers else.

3. Final Answer:

   score = 95, score = 85, and score = 70 -> Option A

4. Quick Check:

   All branches covered by three inputs = 100% coverage [OK]

Hint: Test all branches to cover all statements fully [OK]

Common Mistakes:

• Testing only some branches
• Assuming one input covers all
• Ignoring else branch coverage