Three-way merge in Git - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the base in a three-way merge

In a three-way merge, what role does the 'base' commit play?

A It is the latest commit on the target branch after the merge is complete.

B It is the commit that is discarded during the merge process.

C It is the commit that contains the merge conflict markers.

D It is the common ancestor of the two branches being merged, used to identify changes.

💡 Hint

Think about what helps Git compare changes from two branches.

The base commit is the common ancestor of the two branches. Git uses it to compare changes made in each branch to detect conflicts and merge differences.

💻 Command Output

intermediate

Output of a three-way merge conflict

What output does Git produce when a three-way merge results in a conflict?

Git

git merge feature-branch

A Already up to date.

B Auto-merging file.txt\nCONFLICT (content): Merge conflict in file.txt\nAutomatic merge failed; fix conflicts and then commit the result.

C error: pathspec 'feature-branch' did not match any file(s) known to git

D Merge made by the 'recursive' strategy.\n file.txt | 2 ++\n 1 file changed, 2 insertions(+)

💡 Hint

Look for messages indicating conflicts.

When a merge conflict occurs, Git shows 'CONFLICT' messages and tells you to fix conflicts manually before committing.

🔀 Workflow

advanced

Steps to resolve a three-way merge conflict

Which sequence correctly describes the steps to resolve a three-way merge conflict in Git?

A 1,2,3,4

B 2,1,3,4

C 1,3,2,4

D 3,1,2,4

💡 Hint

Think about the logical order from detecting conflicts to finishing the merge.

First, you check which files have conflicts, then edit them to fix conflicts, stage the fixed files, and finally commit the merge.

❓ Troubleshoot

advanced

Cause of repeated merge conflicts in a three-way merge

You keep getting the same merge conflicts every time you try to merge a feature branch into main. What is the most likely cause?

A You did not stage the resolved files before committing the merge.

B The feature branch was deleted before merging.

C You merged the branches in the wrong order.

D The base commit is missing from the repository.

💡 Hint

Think about what happens if Git does not see your conflict resolutions.

If you fix conflicts but do not stage the files with 'git add', Git thinks conflicts remain and will not complete the merge.

✅ Best Practice

expert

Best practice to minimize three-way merge conflicts

Which practice best helps reduce the chance of complex three-way merge conflicts in a team project?

A Use force push to overwrite remote branches regularly.

B Avoid committing changes until the feature is fully complete.

C Frequently pull and merge changes from the main branch into your feature branch.

D Delete the main branch and work only on feature branches.

💡 Hint

Think about keeping your branch up to date with others' changes.

Regularly merging main into your feature branch keeps your work current and reduces conflicts when merging back.

Practice

1. What is the main purpose of a three-way merge in Git?

easy

A. To combine changes from two branches using a common base

B. To delete a branch after merging

C. To create a new branch from the current branch

D. To reset the current branch to a previous commit

Solution

1. Step 1: Understand the concept of three-way merge

   A three-way merge uses the common ancestor of two branches to combine their changes safely.

2. Step 2: Identify the purpose in Git workflow

   This process helps merge changes from two branches without losing work, especially when both branches have edits.

3. Final Answer:

   To combine changes from two branches using a common base -> Option A

4. Quick Check:

   Three-way merge = combine changes safely [OK]

Hint: Three-way merge combines two branches with a common ancestor [OK]

Common Mistakes:

• Confusing merge with branch deletion
• Thinking merge creates new branches
• Mixing merge with reset commands

2. Which Git command automatically performs a three-way merge when integrating changes from a remote branch?

easy

A. git pull

B. git merge

C. git commit

D. git branch

Solution

1. Step 1: Recall commands that fetch and merge

   git pull fetches changes from a remote branch and merges them locally, often using a three-way merge.

2. Step 2: Differentiate from other commands

   git merge merges branches locally but does not fetch remote changes; git branch manages branches; git commit records changes.

3. Final Answer:

   git pull -> Option A

4. Quick Check:

   git pull = fetch + merge (three-way) [OK]

Hint: git pull fetches and merges remotely with three-way merge [OK]

Common Mistakes:

• Choosing git merge without fetching first
• Confusing git commit with merge
• Using git branch for merging

3. Given the following scenario:

Branch A has file.txt with content: "Hello World"
Branch B modifies file.txt to: "Hello Git"
Common base has file.txt: "Hi World"

What will be the content of file.txt after a successful three-way merge of Branch B into Branch A?

medium

A. "Hello"

B. "Hello Git"

C. "Hello World Git"

D. "Hello World"

Solution

1. Step 1: Identify changes from base to each branch

   Base has "Hi World". Branch A changed "Hi" to "Hello". Branch B changed "Hi" to "Hello" and "World" to "Git".

2. Step 2: Understand three-way merge result

   Since the change "Hi" -> "Hello" is common to both branches, and Branch B has an additional change "World" -> "Git", Git's three-way merge automatically combines them, resulting in "Hello Git".

3. Final Answer:

   "Hello Git" -> Option B

4. Quick Check:

   Three-way merge picks combined changes, here "Hello Git" [OK]

Hint: Merged content reflects changes from both branches via base [OK]

Common Mistakes:

• Assuming content concatenates both changes
• Ignoring base version in merge
• Confusing which branch's changes apply

4. You ran git merge feature but got a conflict in app.js. What should you do to resolve this three-way merge conflict?

medium

A. Run git reset --hard immediately to discard all changes

B. Delete app.js and run git merge --abort

C. Edit app.js to fix conflicts, then run git add app.js and git commit

D. Run git branch -d feature to delete the feature branch

Solution

1. Step 1: Understand merge conflict resolution

   When a conflict occurs, you must manually edit the conflicting file to resolve differences.

2. Step 2: Stage and commit resolved file

   After fixing conflicts in app.js, use git add to stage and then git commit to complete the merge.

3. Final Answer:

   Edit app.js, then git add and git commit -> Option C

4. Quick Check:

   Fix conflicts, stage, commit to resolve merge [OK]

Hint: Fix conflicts manually, then add and commit [OK]

Common Mistakes:

• Deleting files instead of resolving conflicts
• Aborting merge without fixing conflicts
• Deleting branches to fix conflicts

5. You have two branches, main and feature. Both modified the same function in utils.py differently. After running git merge feature into main, a three-way merge conflict occurs. Which approach best resolves this conflict while preserving both changes?

hard

A. Delete feature branch and continue with main unchanged

B. Force merge with git merge --strategy=ours to keep main version only

C. Reset main to the common ancestor commit and retry merge

D. Manually edit utils.py to combine both changes logically, then stage and commit

Solution

1. Step 1: Recognize conflict in same function

   Both branches changed the same function differently, causing a conflict during merge.

2. Step 2: Choose best resolution method

   Manually editing the file to combine both changes logically preserves work from both branches, which is the best practice.

3. Step 3: Stage and commit after resolving

   After editing, stage the file with git add and commit to complete the merge.

4. Final Answer:

   Manually edit utils.py to combine changes, then stage and commit -> Option D

5. Quick Check:

   Manual merge preserves both changes best [OK]

Hint: Edit conflicts to combine changes, then add and commit [OK]

Common Mistakes:

• Using --strategy=ours loses feature changes
• Deleting branches to avoid conflicts
• Resetting loses recent work