feat: Add git branch functionality and unit tests

This commit introduces the `git branch` tool to the MCP Git server, allowing users to list branches with various filtering options.

Changes include:
- Implemented `git_branch` function in `src/git/src/mcp_server_git/server.py` to support listing local, remote, and all branches, as well as filtering by `contains` and `not_contains` SHA values.
- Added comprehensive unit tests for the `git branch` functionality in `src/git/tests/test_server.py`, covering different branch types and commit filtering scenarios.
- Updated `src/git/README.md`.

src/git/src/mcp_server_git/server.py

@@ -1,6 +1,6 @@
 import logging
 from pathlib import Path
-from typing import Sequence
+from typing import Sequence, Optional
 from mcp.server import Server
 from mcp.server.session import ServerSession
 from mcp.server.stdio import stdio_server
@@ -13,7 +13,7 @@ from mcp.types import (
 )
 from enum import Enum
 import git
-from pydantic import BaseModel
+from pydantic import BaseModel, Field
 
 class GitStatus(BaseModel):
     repo_path: str
@@ -59,6 +59,24 @@ class GitShow(BaseModel):
 class GitInit(BaseModel):
     repo_path: str
 
+class GitBranch(BaseModel):
+    repo_path: str = Field(
+        ...,
+        description="The path to the Git repository.",
+    )
+    branch_type: str = Field(
+        ...,
+        description="Whether to list local branches ('local'), remote branches ('remote') or all branches('all').",
+    )
+    contains: Optional[str] = Field(
+        None,
+        description="The commit sha that branch should contain. Do not pass anything to this param if no commit sha is specified",
+    )
+    not_contains: Optional[str] = Field(
+        None,
+        description="The commit sha that branch should NOT contain. Do not pass anything to this param if no commit sha is specified",
+    )
+
 class GitTools(str, Enum):
     STATUS = "git_status"
     DIFF_UNSTAGED = "git_diff_unstaged"
@@ -72,6 +90,7 @@ class GitTools(str, Enum):
     CHECKOUT = "git_checkout"
     SHOW = "git_show"
     INIT = "git_init"
+    BRANCH = "git_branch"
 
 def git_status(repo: git.Repo) -> str:
     return repo.git.status()
@@ -147,6 +166,34 @@ def git_show(repo: git.Repo, revision: str) -> str:
         output.append(d.diff.decode('utf-8'))
     return "".join(output)
 
+def git_branch(repo: git.Repo, branch_type: str, contains: str | None = None, not_contains: str | None = None) -> str:
+    match contains:
+        case None:
+            contains_sha = (None,)
+        case _:
+            contains_sha = ("--contains", contains)
+
+    match not_contains:
+        case None:
+            not_contains_sha = (None,)
+        case _:
+            not_contains_sha = ("--no-contains", not_contains)
+
+    match branch_type:
+        case 'local':
+            b_type = None
+        case 'remote':
+            b_type = "-r"
+        case 'all':
+            b_type = "-a"
+        case _:
+            return f"Invalid branch type: {branch_type}"
+
+    # None value will be auto deleted by GitPython
+    branch_info = repo.git.branch(b_type, *contains_sha, *not_contains_sha)
+
+    return branch_info
+
 async def serve(repository: Path | None) -> None:
     logger = logging.getLogger(__name__)
 
@@ -222,6 +269,11 @@ async def serve(repository: Path | None) -> None:
                 name=GitTools.INIT,
                 description="Initialize a new Git repository",
                 inputSchema=GitInit.schema(),
+            ),
+            Tool(
+                name=GitTools.BRANCH,
+                description="List Git branches",
+                inputSchema=GitBranch.schema(),
             )
         ]
 
@@ -351,6 +403,18 @@ async def serve(repository: Path | None) -> None:
                     text=result
                 )]
 
+            case GitTools.BRANCH:
+                result = git_branch(
+                    repo,
+                    arguments.get("branch_type", 'local'),
+                    arguments.get("contains", None),
+                    arguments.get("not_contains", None),
+                )
+                return [TextContent(
+                    type="text",
+                    text=result
+                )]
+
             case _:
                 raise ValueError(f"Unknown tool: {name}")