Add test for file system initialization methods

Since we now have three rivaling modes of initialization for the file
system, it is time to test the priority order is correct.

This brought up a quirk related to instance caching: Since both the
`lakectl` config file and environment variables are read implicitly,
they do not require arguments, and thus the first method used between
config file and envvar initialization will cause cache hits, and
suffocate the other method unless the cache is cleared.

tests/conftest.py

@@ -7,6 +7,7 @@
 from typing import Generator, TypeVar
 
 import pytest
+import yaml
 from lakefs_client import Configuration
 from lakefs_client.client import LakeFSClient
 from lakefs_client.models import BranchCreation, RepositoryCreation
@@ -107,3 +108,21 @@ def temp_branch(lakefs_client: LakeFSClient, repository: str) -> YieldFixture[st
 @pytest.fixture
 def random_file_factory(tmp_path: Path) -> RandomFileFactory:
     return RandomFileFactory(path=tmp_path)
+
+
+@pytest.fixture
+def temporary_lakectl_config() -> YieldFixture[str]:
+    d = {
+        "credentials": {"access_key_id": "hello", "secret_access_key": "world"},
+        "server": {"endpoint_url": "http://hello-world-xyz"},
+    }
+
+    loc = "~/.lakectl.yaml"
+    path = Path(loc).expanduser()
+
+    try:
+        with open(path, "w") as f:
+            yaml.dump(d, f)
+        yield loc
+    finally:
+        path.unlink()

tests/test_fs.py

@@ -1,3 +1,5 @@
+from pytest import MonkeyPatch
+
 from lakefs_spec import LakeFSFileSystem
 
 
@@ -20,3 +22,43 @@ def test_instance_caching(fs: LakeFSFileSystem) -> None:
 
     assert fs2._fs_token != fs._fs_token
     assert len(LakeFSFileSystem._cache) == 2
+
+
+def test_initialization(monkeypatch: MonkeyPatch, temporary_lakectl_config: str) -> None:
+    """
+    Verify the priority order of initialization in lakeFS file system:
+    1. direct arguments
+    2. environment variables
+    3. `lakectl` config file
+
+    NOTE: The configuration appends "/api/v1" to all hostnames by default.
+    """
+
+    # Verify behaviors in reverse priority order.
+    # Case 1: Instantiation from ~/.lakectl.yaml.
+    cfg_fs = LakeFSFileSystem()
+    config = cfg_fs.client._api.configuration
+    assert config.host == "http://hello-world-xyz/api/v1"
+    assert config.username == "hello"
+    assert config.password == "world"
+
+    monkeypatch.setenv("LAKEFS_HOST", "http://localhost:1000")
+    monkeypatch.setenv("LAKEFS_USERNAME", "my-user")
+    monkeypatch.setenv("LAKEFS_PASSWORD", "my-password-12345")
+
+    # Case 2: Instantiation from envvars.
+    # Clear the instance cache first, since we otherwise would get a cache hit
+    # due to the instantiation being the same as from `.lakectl.yaml` above.
+    LakeFSFileSystem._cache.clear()
+    envvar_fs = LakeFSFileSystem()
+    config = envvar_fs.client._api.configuration
+    assert config.host == "http://localhost:1000/api/v1"
+    assert config.username == "my-user"
+    assert config.password == "my-password-12345"
+
+    # Case 3: Explicit initialization.
+    fs = LakeFSFileSystem(host="http://lakefs.hello", username="my-user", password="my-password")
+    config = fs.client._api.configuration
+    assert config.host == "http://lakefs.hello/api/v1"
+    assert config.username == "my-user"
+    assert config.password == "my-password"