Implement T9L1/create-pr-from-main (#276)

# Exercise Review

## Exercise Discussion

Fixes #274 

## Checklist

- [ ] If you require a new remote repository on the `Git-Mastery`
organization, have you [created a
request](https://github.com/git-mastery/exercises/issues/new?template=request_exercise_repository.yaml)
for it?
- [x] Have you written unit tests using
[`repo-smith`](https://github.com/git-mastery/repo-smith) to validate
the exercise grading scheme?
- [x] Have you tested your changes using the instructions posted?
- [x] Have you verified that this exercise does not already exist or is
not currently in review?
- [ ] Did you introduce a new grading mechanism that should belong to
[`git-autograder`](https://github.com/git-mastery/git-autograder)?
- [ ] Did you introduce a new dependency that should belong to
[`app`](https://github.com/git-mastery/app)?

Author: desmondwong1215

create_pr_from_main/.gitmastery-exercise.json

@@ -0,0 +1,14 @@
+{
+  "exercise_name": "create-pr-from-main",
+  "tags": [],
+  "requires_git": true,
+  "requires_github": true,
+  "base_files": {},
+  "exercise_repo": {
+    "repo_type": "remote",
+    "repo_name": "languages",
+    "repo_title": "gm-languages",
+    "create_fork": true,
+    "init": null
+  }
+}

create_pr_from_main/README.md

@@ -0,0 +1 @@
+See https://git-mastery.org/lessons/prsCreate/exercise-create-pr-from-main.html

create_pr_from_main/__init__.py

@@ -0,0 +1,8 @@
+from pathlib import Path
+
+from exercise_utils.exercise_config import add_pr_config
+from exercise_utils.gitmastery import create_start_tag
+
+def setup(verbose: bool = False):
+    create_start_tag(verbose)
+    add_pr_config(pr_repo_full_name="git-mastery/gm-languages", config_path=Path("../"))

create_pr_from_main/download.py

@@ -0,0 +1,115 @@
+from contextlib import contextmanager
+from unittest.mock import PropertyMock, patch
+
+import pytest
+from exercise_utils.test import GitAutograderTestLoader, assert_output
+from git_autograder import (
+    GitAutograderStatus,
+    GitAutograderWrongAnswerException,
+)
+from git_autograder.pr import GitAutograderPr
+
+from .verify import (
+    EXPECTED_CONTENT_STEP_3,
+    JAVA_FILE_MISSING,
+    JAVA_INVALID_CONTENT,
+    PR_MISSING,
+    WRONG_HEAD_BRANCH,
+    verify,
+)
+
+REPOSITORY_NAME = "create-pr-from-main"
+
+loader = GitAutograderTestLoader(REPOSITORY_NAME, verify)
+
+# NOTE: This exercise is a special case where we do not require repo-smith. Instead,
+# we directly mock function calls to verify that all branches are covered for us.
+
+
+class FakeCommit:
+    def __init__(self, java_content: str | None) -> None:
+        self._java_content = java_content
+
+    @contextmanager
+    def file(self, file_path: str):
+        yield self._java_content
+
+
+def _run_verify(
+    pr_numbers: list[int] | None = None,
+    head_branch: str = "",
+    java_content: str | None = None,
+):
+    if pr_numbers is None:
+        pr_numbers = []
+    fake_commit = FakeCommit(java_content)
+    with (
+        loader.start_mock_exercise(
+            has_pr_context=True, pr_number=1, pr_repo_full_name="dummy/repo"
+        ) as exercise,
+        patch(
+            "create_pr_from_main.verify.get_pr_numbers_by_author",
+            return_value=pr_numbers,
+        ),
+        patch("create_pr_from_main.verify.add_pr_config"),
+        patch.object(exercise, "fetch_pr", return_value=None),
+        patch.object(
+            GitAutograderPr,
+            "head_branch",
+            new_callable=PropertyMock,
+            return_value=head_branch,
+        ),
+        patch.object(
+            GitAutograderPr,
+            "last_user_commit",
+            new_callable=PropertyMock,
+            return_value=fake_commit,
+        ),
+    ):
+        return verify(exercise)
+
+
+def test_success():
+    output = _run_verify(
+        pr_numbers=[123],
+        head_branch="main",
+        java_content="\n".join(EXPECTED_CONTENT_STEP_3),
+    )
+
+    assert_output(output, GitAutograderStatus.SUCCESSFUL)
+
+
+def test_pr_missing():
+    with pytest.raises(GitAutograderWrongAnswerException) as exception:
+        _run_verify()
+
+    assert exception.value.message == [PR_MISSING]
+
+
+def test_wrong_head_branch():
+    with pytest.raises(GitAutograderWrongAnswerException) as exception:
+        _run_verify(pr_numbers=[1], head_branch="feature/pr-branch")
+
+    assert exception.value.message == [WRONG_HEAD_BRANCH]
+
+
+def test_java_file_missing():
+    with pytest.raises(GitAutograderWrongAnswerException) as exception:
+        _run_verify(
+            pr_numbers=[1],
+            head_branch="main",
+            java_content=None,
+        )
+
+    assert exception.value.message == [JAVA_FILE_MISSING]
+
+
+def test_java_content_invalid():
+    with pytest.raises(GitAutograderWrongAnswerException) as exception:
+        _run_verify(
+            pr_numbers=[1],
+            head_branch="main",
+            java_content="wrong content\n",
+        )
+
+    assert exception.value.message == [JAVA_INVALID_CONTENT]

create_pr_from_main/test_verify.py

@@ -0,0 +1,55 @@
+from pathlib import Path
+
+from git_autograder import (
+    GitAutograderOutput,
+    GitAutograderExercise,
+    GitAutograderStatus,
+)
+
+from exercise_utils.exercise_config import add_pr_config
+from exercise_utils.github_cli import get_github_username, get_pr_numbers_by_author
+
+
+JAVA_FILE_MISSING = "Java.txt file is missing in the latest commit on main branch."
+JAVA_INVALID_CONTENT = "The content in Java.txt in main branch is not correct."
+MULTIPLE_PRS = "Multiple PRs found. The latest pr will be used in grading."
+PR_MISSING = "No PR is found."
+WRONG_HEAD_BRANCH = "The PR's head branch is not 'main'."
+
+
+EXPECTED_CONTENT_STEP_3 = ["1995, by James Gosling"]
+
+
+def verify(exercise: GitAutograderExercise) -> GitAutograderOutput:
+    username = get_github_username(False)
+    target_repo = f"git-mastery/{exercise.config.exercise_repo.repo_title}"
+    comments = []
+
+    pr_numbers = get_pr_numbers_by_author(username, target_repo, False)
+    if not pr_numbers:
+        raise exercise.wrong_answer([PR_MISSING])
+    if len(pr_numbers) > 1:
+        comments.append(MULTIPLE_PRS)
+    pr_number = pr_numbers[-1]
+
+    add_pr_config(pr_number=pr_number, config_path=Path("./"))
+    exercise.fetch_pr()
+
+    if exercise.repo.prs.pr.head_branch != "main":
+        comments.append(WRONG_HEAD_BRANCH)
+        raise exercise.wrong_answer(comments)
+
+    latest_user_commit = exercise.repo.prs.pr.last_user_commit
+    with latest_user_commit.file("Java.txt") as content:
+        if content is None:
+            comments.append(JAVA_FILE_MISSING)
+            raise exercise.wrong_answer(comments)
+        extracted_content = [
+            line.strip() for line in content.splitlines() if line.strip() != ""
+        ]
+    if extracted_content != EXPECTED_CONTENT_STEP_3:
+        comments.append(JAVA_INVALID_CONTENT)
+        raise exercise.wrong_answer(comments)
+
+    comments.append("Good job creating the PR and pushing commits!")
+    return exercise.to_output(comments, GitAutograderStatus.SUCCESSFUL)