- A
Use Cloud Build with a step that caches test results based on file hashes.
Why wrong: Caching can reduce runtime but still runs tests on all files initially.
- B
Use Cloud Build with a step that runs all tests in parallel.
Why wrong: Running all tests in parallel improves speed but does not selectively test only changed code.
- C
Use Cloud Build with a step that uses `git log` to find changed files and run tests.
Why wrong: Using `git log` is less precise than `git diff` and may miss uncommitted changes.
- D
Use Cloud Build with a step that checks `git diff` against the previous commit and runs tests only on affected modules using a test runner that supports file-based filtering.
This approach directly targets changed files, minimizing test execution time.
Question 287 of 999
Optimizing CI Pipelines with Selective Test Execution Using Git Diff
This PCD practice question tests your understanding of building and testing applications. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: git diff. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company needs to build a CI/CD pipeline for a microservices architecture. They want to run unit tests quickly by only testing code that has changed. Which approach should they use?
Quick Answer
The answer is to use Cloud Build with a step that checks `git diff` against the previous commit and runs tests only on affected modules using a test runner that supports file-based filtering. This approach is correct because it directly implements selective test execution, allowing the CI pipeline to skip unchanged code and dramatically reduce build times by running only changed code tests in CI with Cloud Build. On the Google Professional Cloud Developer exam, this scenario tests your understanding of optimizing CI/CD pipelines for microservices, where full test suites are too slow; the common trap is assuming parallel execution (Option A) is sufficient, but it still runs all tests, wasting resources. Remember the memory tip: "diff to decide"—use git diff to determine what changed, then test only that scope for maximum efficiency.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use Cloud Build with a step that checks `git diff` against the previous commit and runs tests only on affected modules using a test runner that supports file-based filtering.
Option D is correct because it uses `git diff` to identify only the files that have changed and then runs tests on the affected modules, which is the most efficient approach for selective testing. Option A is not ideal because implementing a custom caching mechanism based on file hashes is complex and may not reliably skip tests when dependencies change. Option B runs all tests in parallel, but that does not reduce the test scope—it still runs the full test suite. Option C uses `git log`, which provides commit history rather than a direct diff of the current changes, making it less precise than `git diff` for identifying changed files.
Key principle: git diff
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use Cloud Build with a step that caches test results based on file hashes.
Why it's wrong here
Caching can reduce runtime but still runs tests on all files initially.
- ✗
Use Cloud Build with a step that runs all tests in parallel.
Why it's wrong here
Running all tests in parallel improves speed but does not selectively test only changed code.
- ✗
Use Cloud Build with a step that uses `git log` to find changed files and run tests.
Why it's wrong here
Using `git log` is less precise than `git diff` and may miss uncommitted changes.
- ✓
Use Cloud Build with a step that checks `git diff` against the previous commit and runs tests only on affected modules using a test runner that supports file-based filtering.
Why this is correct
This approach directly targets changed files, minimizing test execution time.
Related concept
git diff
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- git diff
- Selective testing
- Cloud Build custom step
- Test runner with file-based filtering
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
git diff
Real-world example
How this comes up in practice
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. git diff Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
Review git diff, then practise related PCD questions on the same topic to reinforce the concept.
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Building and testing applications — study guide chapter
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FAQ
Questions learners often ask
What does this PCD question test?
Building and testing applications — This question tests Building and testing applications — git diff.
What is the correct answer to this question?
The correct answer is: Use Cloud Build with a step that checks `git diff` against the previous commit and runs tests only on affected modules using a test runner that supports file-based filtering. — Option D is correct because it uses `git diff` to identify only the files that have changed and then runs tests on the affected modules, which is the most efficient approach for selective testing. Option A is not ideal because implementing a custom caching mechanism based on file hashes is complex and may not reliably skip tests when dependencies change. Option B runs all tests in parallel, but that does not reduce the test scope—it still runs the full test suite. Option C uses `git log`, which provides commit history rather than a direct diff of the current changes, making it less precise than `git diff` for identifying changed files.
What should I do if I get this PCD question wrong?
Review git diff, then practise related PCD questions on the same topic to reinforce the concept.
What is the key concept behind this question?
git diff
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Last reviewed: Jun 24, 2026
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