diff --git a/git_sync/git.py b/git_sync/git.py
index 3ce18cc..68afe50 100644
--- a/git_sync/git.py
+++ b/git_sync/git.py
@@ -182,7 +182,7 @@ async def update_merged_pr_branch(
             await git("branch", "-D", branch_name)
         else:
             await git("reset", "--hard", merged_hash)
-    else:  # noqa: PLR5501
+    else:
         if allow_delete and not await branch_is_an_upstream(branch_name):
             await git("branch", "-D", branch_name)
         else:
diff --git a/git_sync/github.py b/git_sync/github.py
index 0045a07..92d2f8f 100644
--- a/git_sync/github.py
+++ b/git_sync/github.py
@@ -140,7 +140,9 @@ async def fetch_pull_requests_from_domain(
             pr_initial_query(repo.owner, repo.name) for i, repo in enumerate(repos, 1)
         ]
         initial_response = await client.query(join_queries(initial_queries))
-        assert not initial_response.errors
+        if initial_response.errors:
+            msg = f"GraphQL query failed: {initial_response.errors}"
+            raise RuntimeError(msg)
 
         # Determine what follow-up queries to make
         details_queries = [
@@ -149,9 +151,15 @@ async def fetch_pull_requests_from_domain(
             for pr_data in repo_data["pullRequests"]["nodes"]
         ]
 
+        # If there are no PRs, make no follow-up query
+        if not details_queries:
+            return
+
         # Query for detailed PR information
         details_response = await client.query(join_queries(details_queries))
-        assert not details_response.errors
+        if details_response.errors:
+            msg = f"GraphQL query failed: {details_response.errors}"
+            raise RuntimeError(msg)
 
         # Yield response data as PullRequest objects
         for pr_data in details_response.data.values():
diff --git a/pyproject.toml b/pyproject.toml
index ef17650..d1d6769 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [project]
 name = "git-sync"
-version = "0.4.2"
+version = "0.4.3"
 description = "Synchronize local git repo with remotes"
 authors = [{ name = "Alice Purcell", email = "alicederyn@gmail.com" }]
 requires-python = ">= 3.12"
@@ -21,7 +21,8 @@ asyncio_mode = "auto"
 target-version = "py310"
 
 [tool.ruff.lint]
-select = ["ANN", "B", "C4", "E", "F", "I", "PGH", "PLR", "PYI", "RUF", "SIM", "UP", "W"]
+select = ["ANN", "B", "C4", "E", "F", "I", "PGH", "PL", "PYI", "RUF", "SIM", "UP", "W"]
+ignore = ["PLR"]
 isort.split-on-trailing-comma = false
 
 [tool.setuptools.dynamic]
diff --git a/tests/test_github.py b/tests/test_github.py
new file mode 100644
index 0000000..78e4fe1
--- /dev/null
+++ b/tests/test_github.py
@@ -0,0 +1,245 @@
+from collections.abc import Iterator
+from unittest.mock import AsyncMock, Mock, patch
+
+import pytest
+
+from git_sync.github import PullRequest, Repository, fetch_pull_requests_from_domain
+
+TWO_REPOS = [
+    Repository(domain="github.com", owner="owner1", name="repo1"),
+    Repository(domain="github.com", owner="owner2", name="repo2"),
+]
+
+
+@pytest.fixture(autouse=True)
+def graphql_client() -> Iterator[Mock]:
+    mock_client = AsyncMock(name="graphql-client")
+    mock_client.query.return_value = Mock(
+        data={"q0": {"pullRequests": {"nodes": []}}},
+        errors=None,
+    )
+    with patch("git_sync.github.GraphQLClient") as mock:
+        mock.return_value = mock_client
+        yield mock
+
+
+@pytest.fixture(autouse=True)
+def client_session() -> Iterator[Mock]:
+    session = Mock(name="client_session")
+    with patch("git_sync.github.client_session") as mock:
+        mock.return_value.__aenter__ = AsyncMock(return_value=session)
+        mock.return_value.__aexit__ = AsyncMock(return_value=None)
+        yield session
+
+
+async def test_successful_fetch_with_multiple_repos_and_prs(
+    graphql_client: Mock,
+) -> None:
+    """Test successful fetching of PRs from multiple repositories."""
+    initial_data = {
+        "q0": {
+            "pullRequests": {
+                "nodes": [
+                    {"id": "pr1", "commits": {"totalCount": 3}},
+                    {"id": "pr2", "commits": {"totalCount": 1}},
+                ]
+            }
+        },
+        "q1": {
+            "pullRequests": {
+                "nodes": [
+                    {"id": "pr3", "commits": {"totalCount": 2}},
+                ]
+            }
+        },
+    }
+
+    details_data = {
+        "q0": {
+            "headRefName": "feature-branch-1",
+            "headRepository": {
+                "sshUrl": "git@github.com:owner1/repo1.git",
+                "url": "https://github.com/owner1/repo1",
+            },
+            "commits": {
+                "nodes": [
+                    {"commit": {"oid": "commit1"}},
+                    {"commit": {"oid": "commit2"}},
+                    {"commit": {"oid": "commit3"}},
+                ]
+            },
+            "mergeCommit": {"oid": "merge1"},
+        },
+        "q1": {
+            "headRefName": "feature-branch-2",
+            "headRepository": {
+                "sshUrl": "git@github.com:owner1/repo1.git",
+                "url": "https://github.com/owner1/repo1",
+            },
+            "commits": {
+                "nodes": [
+                    {"commit": {"oid": "commit4"}},
+                ]
+            },
+            "mergeCommit": None,
+        },
+        "q2": {
+            "headRefName": "feature-branch-3",
+            "headRepository": {
+                "sshUrl": "git@github.com:owner2/repo2.git",
+                "url": "https://github.com/owner2/repo2",
+            },
+            "commits": {
+                "nodes": [
+                    {"commit": {"oid": "commit5"}},
+                    {"commit": {"oid": "commit6"}},
+                ]
+            },
+            "mergeCommit": {"oid": "merge2"},
+        },
+    }
+
+    graphql_client.return_value.query.side_effect = [
+        Mock(data=initial_data, errors=None),
+        Mock(data=details_data, errors=None),
+    ]
+
+    # Execute the function
+    result = []
+    async for pr in fetch_pull_requests_from_domain(Mock(), "github.com", TWO_REPOS):
+        result.append(pr)
+
+    # Verify results
+    assert len(result) == 3
+
+    # First PR - with merge commit, commits in reverse order (newest first)
+    assert result[0] == PullRequest(
+        branch_name="feature-branch-1",
+        repo_urls=frozenset(
+            [
+                "git@github.com:owner1/repo1.git",
+                "https://github.com/owner1/repo1",
+                "https://github.com/owner1/repo1.git",
+            ]
+        ),
+        hashes=("commit3", "commit2", "commit1"),  # Newest first
+        merged_hash="merge1",
+    )
+
+    # Second PR - without merge commit
+    assert result[1] == PullRequest(
+        branch_name="feature-branch-2",
+        repo_urls=frozenset(
+            [
+                "git@github.com:owner1/repo1.git",
+                "https://github.com/owner1/repo1",
+                "https://github.com/owner1/repo1.git",
+            ]
+        ),
+        hashes=("commit4",),
+        merged_hash=None,
+    )
+
+    # Third PR - from different repo
+    assert result[2] == PullRequest(
+        branch_name="feature-branch-3",
+        repo_urls=frozenset(
+            [
+                "git@github.com:owner2/repo2.git",
+                "https://github.com/owner2/repo2",
+                "https://github.com/owner2/repo2.git",
+            ]
+        ),
+        hashes=("commit6", "commit5"),
+        merged_hash="merge2",
+    )
+
+
+async def test_public_github_endpoint(
+    graphql_client: Mock, client_session: Mock
+) -> None:
+    async for _ in fetch_pull_requests_from_domain(
+        "test-token", "github.com", TWO_REPOS
+    ):
+        pass
+
+    graphql_client.assert_called_once_with(
+        endpoint="https://api.github.com/graphql",
+        headers={"Authorization": "Bearer test-token"},
+        session=client_session,
+    )
+
+
+async def test_github_enterprise_endpoint(
+    graphql_client: Mock, client_session: Mock
+) -> None:
+    async for _ in fetch_pull_requests_from_domain(
+        "test-token", "github.example.com", TWO_REPOS
+    ):
+        pass
+
+    graphql_client.assert_called_once_with(
+        endpoint="https://github.example.com/api/graphql",
+        headers={"Authorization": "Bearer test-token"},
+        session=client_session,
+    )
+
+
+async def test_no_pull_requests_found(graphql_client: Mock) -> None:
+    graphql_client.return_value.query.return_value.data = {
+        "q0": {"pullRequests": {"nodes": []}},
+        "q1": {"pullRequests": {"nodes": []}},
+    }
+
+    async for _ in fetch_pull_requests_from_domain(Mock(), Mock(), TWO_REPOS):
+        raise AssertionError("Should not yield any pull requests")
+
+    graphql_client.return_value.query.assert_called_once()
+
+
+async def test_pr_without_head_repository(graphql_client: Mock) -> None:
+    """Test handling of PR without head repository (e.g. from deleted fork)."""
+    initial_data = {
+        "q0": {
+            "pullRequests": {
+                "nodes": [
+                    {"id": "pr1", "commits": {"totalCount": 1}},
+                ]
+            }
+        },
+    }
+
+    details_data = {
+        "q0": {
+            "headRefName": "feature-branch",
+            "headRepository": None,  # Deleted repository
+            "commits": {
+                "nodes": [
+                    {"commit": {"oid": "commit1"}},
+                ]
+            },
+            "mergeCommit": None,
+        },
+    }
+
+    graphql_client.return_value.query.side_effect = [
+        Mock(data=initial_data, errors=None),
+        Mock(data=details_data, errors=None),
+    ]
+
+    result = []
+    async for pr in fetch_pull_requests_from_domain(Mock(), Mock(), [TWO_REPOS[0]]):
+        result.append(pr)
+
+    # Should still create PR but with empty repo URLs
+    assert len(result) == 1
+    assert result[0].repo_urls == frozenset()
+    assert result[0].branch_name == "feature-branch"
+
+
+async def test_graphql_errors(graphql_client: Mock) -> None:
+    graphql_client.return_value.query.return_value = Mock(errors=["Some GraphQL error"])
+
+    with pytest.raises(RuntimeError, match="GraphQL query failed:"):
+        async for _ in fetch_pull_requests_from_domain(Mock(), Mock(), TWO_REPOS):
+            pass