Implement exercise T6L1/branch-previous

branch_previous/.gitmastery-exercise.json

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+{
+  "exercise_name": "branch-previous",
+  "tags": [
+    "git-branch"
+  ],
+  "requires_git": true,
+  "requires_github": false,
+  "base_files": {},
+  "exercise_repo": {
+    "repo_type": "local",
+    "repo_name": "horror-story",
+    "repo_title": null,
+    "create_fork": null,
+    "init": true
+  }
+}

branch_previous/README.md

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+# branch-previous
+
+You are writing the outline for a story, in `story.txt`.
+
+You have written the first few steps of the storyline.
+
+You are not very happy with the way the story is progressing, and wish to explore a few alternative storylines starting from a previous step.
+
+## Task
+
+1. Start a new branch named `visitor-line`, starting from the second commit (i.e., commit `Add second line`).
+2. Add the line `I heard someone knocking at the door`. to the `story.txt`.
+3. Commit the change. You may use any suitable commit message.
+4. Start a new branch named `sleep-line`, starting from the same starting point as before.
+5. Add the line `I fell asleep on the couch`. to the `story.txt`.
+6. Commit the change. You may use any suitable commit message.
+
+## Expected Revision Graph
+
+```mermaid
+gitGraph BT:
+  commit id: "Describe night"
+  commit id: "Describe location"
+  branch visitor-line
+  checkout main
+  branch sleep-line
+  checkout main
+  commit id: "Mention noise"
+  checkout visitor-line
+  commit id: "Mention knocking"
+  checkout sleep-line
+  commit id: "Mention sleeping"
+```

branch_previous/download.py

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+from exercise_utils.file import create_or_update_file, append_to_file
+from exercise_utils.git import add, commit
+
+def setup(verbose: bool = False):
+    create_or_update_file(
+        "story.txt",
+        """
+        It was a dark and stormy night.
+        """
+    )
+    add(["story.txt"], verbose)
+    commit("Describe night", verbose)
+
+    append_to_file(
+        "story.txt", 
+        """
+        I was alone in my room.
+        """
+    )
+    add(["story.txt"], verbose)
+    commit("Describe location", verbose)
+
+    append_to_file(
+        "story.txt",
+        """
+        I heard a strange noise.
+        """
+    )
+    add(["story.txt"], verbose)
+    commit("Mention noise", verbose)

branch_previous/tests/specs/base.yml

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+initialization:
+  steps:
+    - type: new-file
+      filename: story.txt
+      contents: "It was a dark and stormy night.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Describe night
+      id: start
+    - type: append-file
+      filename: story.txt
+      contents: "I was alone in my room.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Describe location
+      empty: false
+      id: describe_location_commit
+    - type: append-file
+      filename: story.txt
+      contents: "I heard a strange noise.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Mention noise
+      empty: false
+    - type: bash
+      runs: git checkout -b visitor-line HEAD~1
+    - type: append-file
+      filename: story.txt
+      contents: "I heard someone knocking at the door.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Mention knocking
+      empty: false
+    - type: bash
+      runs: git checkout -b sleep-line HEAD~1
+    - type: append-file
+      filename: story.txt
+      contents: "I fell asleep on the couch.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Mention sleeping
+      empty: false

branch_previous/tests/specs/sleep_missing_branch.yml

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+initialization:
+  steps:
+    - type: new-file
+      filename: story.txt
+      contents: "It was a dark and stormy night.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Describe night
+      empty: false
+      id: start
+    - type: append-file
+      filename: story.txt
+      contents: "I was alone in my room.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Describe location
+      empty: false
+      id: describe_location_commit
+    - type: append-file
+      filename: story.txt
+      contents: "I heard a strange noise.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Mention noise
+      empty: false
+    # Only create visitor-line branch, not sleep-line
+    - type: bash
+      runs: git checkout -b visitor-line HEAD~1
+    - type: append-file
+      filename: story.txt
+      contents: "I heard someone knocking at the door.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Mention knocking
+      empty: false

branch_previous/tests/specs/sleep_wrong_content.yml

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+initialization:
+  steps:
+    - type: new-file
+      filename: story.txt
+      contents: "It was a dark and stormy night.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Describe night
+      empty: false
+      id: start
+    - type: append-file
+      filename: story.txt
+      contents: "I was alone in my room.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Describe location
+      empty: false
+      id: describe_location_commit
+    - type: append-file
+      filename: story.txt
+      contents: "I heard a strange noise.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Mention noise
+      empty: false
+    - type: bash
+      runs: git checkout -b visitor-line HEAD~1
+    - type: append-file
+      filename: story.txt
+      contents: "I heard someone knocking at the door.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Mention knocking
+      empty: false
+    - type: bash
+      runs: git checkout -b sleep-line HEAD~1
+    - type: append-file
+      filename: story.txt
+      contents: "Wrong content here.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Mention sleeping
+      empty: false

branch_previous/tests/specs/visitor_missing_branch.yml

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+initialization:
+  steps:
+    - type: new-file
+      filename: story.txt
+      contents: "It was a dark and stormy night.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Describe night
+      id: start
+    - type: append-file
+      filename: story.txt
+      contents: "I was alone in my room.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Describe location
+      empty: false
+      id: second_commit
+    - type: append-file
+      filename: story.txt
+      contents: "I heard a strange noise.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Mention noise
+      empty: false
+    # Only create sleep-line branch, not visitor-line
+    - type: bash
+      runs: git checkout -b sleep-line HEAD~1
+    - type: append-file
+      filename: story.txt
+      contents: "I fell asleep on the couch.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Mention sleeping
+      empty: false

branch_previous/tests/specs/visitor_missing_commit.yml

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+initialization:
+  steps:
+    - type: new-file
+      filename: story.txt
+      contents: "It was a dark and stormy night.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Describe night
+      empty: false
+      id: start
+    - type: append-file
+      filename: story.txt
+      contents: "I was alone in my room.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Describe location
+      empty: false
+      id: describe_location_commit
+    - type: append-file
+      filename: story.txt
+      contents: "I heard a strange noise.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Mention noise
+      empty: false
+    # visitor-line branch created but no commit made
+    - type: bash
+      runs: git checkout -b visitor-line HEAD~1
+    # sleep-line branch created with commit
+    - type: bash
+      runs: git checkout -b sleep-line
+    - type: append-file
+      filename: story.txt
+      contents: "I fell asleep on the couch.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Mention sleeping
+      empty: false

branch_previous/tests/specs/visitor_wrong_content.yml

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+initialization:
+  steps:
+    - type: new-file
+      filename: story.txt
+      contents: "It was a dark and stormy night.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Describe night
+      empty: false
+      id: start
+    - type: append-file
+      filename: story.txt
+      contents: "I was alone in my room.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Describe location
+      empty: false
+      id: describe_location_commit
+    - type: append-file
+      filename: story.txt
+      contents: "I heard a strange noise.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Mention noise
+      empty: false
+    - type: bash
+      runs: git checkout -b visitor-line HEAD~1
+    - type: append-file
+      filename: story.txt
+      contents: "Wrong content here.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Mention knocking
+      empty: false
+    - type: bash
+      runs: git checkout -b sleep-line HEAD~1
+    - type: append-file
+      filename: story.txt
+      contents: "I fell asleep on my couch.\n"
+    - type: add
+      files:
+        - story.txt
+    - type: commit
+      message: Mention sleeping
+      empty: false