Implement exercise T6L2/ff-undo

ff_undo/.gitmastery-exercise.json

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+{
+  "exercise_name": "ff-undo",
+  "tags": [
+    "git-branch",
+    "git-merge",
+    "git-reset"
+  ],
+  "requires_git": true,
+  "requires_github": false,
+  "base_files": {},
+  "exercise_repo": {
+    "repo_type": "local",
+    "repo_name": "play-characters",
+    "repo_title": null,
+    "create_fork": null,
+    "init": true
+  }
+}

ff_undo/README.md

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+# ff-undo
+
+This exercise focuses on **undoing a merge in Git**. You will practice how to revert unwanted merge commits while keeping branches and commits intact.
+
+## Task
+
+You have a repository with two branches:
+
+- `main` branch, which initially contains commits:
+  - `Add Rick`
+  - `Add Morty`
+- `others` branch, which contains commits:
+  - `Add Birdperson`
+  - `Add Cyborg to birdperson.txt`
+  - `Add Tammy`
+
+A merge with fast forward from `others` into `main` has been done incorrectly. Your task is:
+
+1. **Undo the merge on `main`**, so that only `Add Rick` and `Add Morty` remain on `main`.
+2. Ensure the `others` branch still exists with all its commits intact.
+3. Do not delete any commits; only undo the merge on `main`.
+
+## Hints
+
+<details>
+<summary>Hint 1: Check your branches</summary>
+
+Use `git branch` to see the current branches and verify `main` and `others` exist.
+</details>
+
+<details>
+<summary>Hint 2: View commit history</summary>
+
+Use `git log --oneline` on `main` to identify the merge commit that needs to be undone.
+</details>
+
+<details>
+<summary>Hint 3: Undo the merge</summary>
+
+You can undo a merge using: `git reset --hard <commit-before-merge>`
+</details>

ff_undo/download.py

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+from exercise_utils.git import (
+    add,
+    commit,
+    checkout,
+    merge_with_message,
+)
+from exercise_utils.file import (
+    create_or_update_file,
+    append_to_file,
+)
+
+def setup(verbose: bool = False):
+    # Create initial files and commits
+    create_or_update_file("rick.txt", "Scientist\n")
+    add(["rick.txt"], verbose)
+    commit("Add Rick", verbose)
+
+    create_or_update_file("morty.txt", "Boy\n")
+    add(["morty.txt"], verbose)
+    commit("Add Morty", verbose)
+
+    # Create and switch to branch 'others'
+    checkout("others", create_branch=True, verbose=verbose)
+
+    create_or_update_file("birdperson.txt", "No job\n")
+    add(["birdperson.txt"], verbose)
+    commit("Add Birdperson", verbose)
+
+    append_to_file("birdperson.txt", "Cyborg\n")
+    add(["birdperson.txt"], verbose)
+    commit("Add Cyborg to birdperson.txt", verbose)
+
+    create_or_update_file("tammy.txt", "Spy\n")
+    add(["tammy.txt"], verbose)
+    commit("Add Tammy", verbose)
+
+    # Merge back into main
+    checkout("main", create_branch=False, verbose=verbose)
+    merge_with_message("others", ff=True, message="Introduce others", verbose=verbose)

ff_undo/tests/specs/base.yml

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+initialization:
+  steps:
+    - type: commit
+      id: start
+      message: "Add Rick"
+    - type: commit
+      message: "Add Morty"
+    - type: branch
+      branch-name: others
+    - type: checkout
+      branch-name: others
+    - type: commit
+      message: "Add Birdperson"
+    - type: commit
+      message: "Add Cyborg to birdperson.txt"
+    - type: commit
+      message: "Add Tammy"
+    - type: checkout
+      branch-name: main

ff_undo/tests/specs/branch_missing.yml

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+initialization:
+  steps:
+    - type: commit
+      id: start
+      message: "Add Rick"
+    - type: commit
+      message: "Add Morty"

ff_undo/tests/specs/main_commits_incorrect.yml

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+initialization:
+  steps:
+    - type: commit
+      id: start
+      message: "Add Morty"
+    - type: branch
+      branch-name: others
+    - type: checkout
+      branch-name: others
+    - type: commit
+      message: "Add Birdperson"
+    - type: commit
+      message: "Add Cyborg to birdperson.txt"
+    - type: commit
+      message: "Add Tammy"

ff_undo/tests/specs/merge_not_undone.yml

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+initialization:
+  steps:
+    - type: commit
+      id: start
+      message: "Add Rick"
+    - type: commit
+      message: "Add Morty"
+    - type: branch
+      branch-name: others
+    - type: checkout
+      branch-name: others
+    - type: commit
+      message: "Add Birdperson"
+    - type: commit
+      message: "Add Cyborg to birdperson.txt"
+    - type: commit
+      message: "Add Tammy"
+    - type: checkout
+      branch-name: main
+    - type: merge
+      branch-name: others
+      no-ff: false
+      message: "Introduce others"

ff_undo/tests/specs/others_commits_incorrect.yml

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+initialization:
+  steps:
+    - type: commit
+      id: start
+      message: "Add Rick"
+    - type: commit
+      message: "Add Morty"
+    - type: branch
+      branch-name: others
+    - type: checkout
+      branch-name: others
+    - type: commit
+      message: "Add Birdperson"
+    - type: commit
+      message: "Add Tammy"

ff_undo/tests/test_verify.py

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+from git_autograder import GitAutograderTestLoader, assert_output
+from git_autograder.status import GitAutograderStatus
+from ..verify import ( 
+    MERGE_NOT_UNDONE,
+    MAIN_COMMITS_INCORRECT,
+    OTHERS_COMMITS_INCORRECT,
+    OTHERS_BRANCH_MISSING,
+    verify
+)
+
+REPOSITORY_NAME = "ff-undo"
+
+loader = GitAutograderTestLoader(__file__, REPOSITORY_NAME, verify)
+
+def test_correct_solution():
+    with loader.load("specs/base.yml") as output:
+        assert_output(output, GitAutograderStatus.SUCCESSFUL)
+
+
+def test_merge_not_undone():
+    with loader.load("specs/merge_not_undone.yml") as output:
+        assert_output(output, GitAutograderStatus.UNSUCCESSFUL, [MERGE_NOT_UNDONE])
+
+
+def test_branch_missing():
+    with loader.load("specs/branch_missing.yml") as output:
+        assert_output(output, GitAutograderStatus.UNSUCCESSFUL, [OTHERS_BRANCH_MISSING])
+
+
+def test_main_commits_incorrect():
+    with loader.load("specs/main_commits_incorrect.yml") as output:
+        assert_output(output, GitAutograderStatus.UNSUCCESSFUL, [MAIN_COMMITS_INCORRECT])
+
+
+def test_others_commits_incorrect():
+    with loader.load("specs/others_commits_incorrect.yml") as output:
+        assert_output(output, GitAutograderStatus.UNSUCCESSFUL, [OTHERS_COMMITS_INCORRECT])

ff_undo/verify.py

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+from git_autograder import (
+    GitAutograderOutput,
+    GitAutograderExercise,
+    GitAutograderStatus,
+)
+
+ADD_RICK = "Add Rick"
+ADD_MORTY = "Add Morty"
+ADD_BIRDPERSON = "Add Birdperson"
+ADD_CYBORG = "Add Cyborg to birdperson.txt"
+ADD_TAMMY = "Add Tammy"
+
+MERGE_NOT_UNDONE = (
+    "You need to undo the merge."
+)
+MAIN_COMMITS_INCORRECT = (
+    "The main branch does not contain the expected commits "
+    "The main branch does not contain both commits 'Add Rick' and 'Add Morty'."
+)
+OTHERS_COMMITS_INCORRECT = (
+    "The others branch does not contain the expected commits "
+    "'Add Birdperson', 'Add Cyborg to birdperson.txt', and 'Add Tammy'."
+)
+OTHERS_BRANCH_MISSING = (
+    "The branch 'others' no longer exists. You should not delete it, only undo the merge on main."
+)
+
+def verify(exercise: GitAutograderExercise) -> GitAutograderOutput:
+    # Get branches
+    main_branch = exercise.repo.branches.branch("main")
+    others_branch = exercise.repo.branches.branch_or_none("others")
+
+    # Check if branch others exists
+    if others_branch is None:
+        raise exercise.wrong_answer([OTHERS_BRANCH_MISSING])
+
+    # Take all commit messages on main
+    commit_messages_in_main = [c.commit.message.strip() for c in main_branch.commits]
+
+    # Take all commit messages on others
+    commit_messages_in_others = [c.commit.message.strip() for c in others_branch.commits]
+
+    # Check that the merge commit is not present on main
+    if any(msg in commit_messages_in_main for msg in [ADD_BIRDPERSON, ADD_CYBORG, ADD_TAMMY]):
+        raise exercise.wrong_answer([MERGE_NOT_UNDONE])
+
+    # Check that commits in main are only the initial 2 commits
+    if len(commit_messages_in_main) != 2 or not all(
+        msg in commit_messages_in_main for msg in [ADD_RICK, ADD_MORTY]
+    ):
+        raise exercise.wrong_answer([MAIN_COMMITS_INCORRECT])
+
+    # Check that commits in others are only the initial 3 commits
+    if len(commit_messages_in_others) != 5 or not all(
+        msg in commit_messages_in_others for msg in [ADD_BIRDPERSON, ADD_CYBORG, ADD_TAMMY]
+    ):
+        raise exercise.wrong_answer([OTHERS_COMMITS_INCORRECT])
+
+    return exercise.to_output(
+        ["You have successfully undone the merge of branch 'others'."],
+        GitAutograderStatus.SUCCESSFUL,
+    )