diff --git a/src/cmake_language_server/server.py b/src/cmake_language_server/server.py
index 1fd0786..bfb69ae 100644
--- a/src/cmake_language_server/server.py
+++ b/src/cmake_language_server/server.py
@@ -23,8 +23,8 @@ class CMakeLanguageServer(LanguageServer):
     _parser: ListParser
     _api: API
 
-    def __init__(self):
-        super().__init__()
+    def __init__(self, *args):
+        super().__init__(*args)
 
         self._parser = ListParser()
         self._api = None
diff --git a/tests/conftest.py b/tests/conftest.py
index 236ced0..aafea51 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -1,9 +1,19 @@
+import asyncio
+import logging
+import os
+import pprint
+from subprocess import PIPE, run
+from threading import Thread
+
 import pytest
+from pygls import features
+from pygls.server import LanguageServer
+
+from cmake_language_server.server import CMakeLanguageServer
 
 
 @pytest.fixture()
 def cmake_build(shared_datadir):
-    from subprocess import run, PIPE
     source = shared_datadir / 'cmake'
     build = source / 'build'
     build.mkdir()
@@ -13,11 +23,37 @@ def cmake_build(shared_datadir):
             stderr=PIPE,
             universal_newlines=True)
     if p.returncode != 0:
-        import logging
-        import os
-        import pprint
         logging.error('env:\n' + pprint.pformat(os.environ))
         logging.error('stdout:\n' + p.stdout)
         logging.error('stderr:\n' + p.stderr)
         raise RuntimeError("CMake failed")
     yield build
+
+
+@pytest.fixture()
+def client_server():
+    c2s_r, c2s_w = os.pipe()
+    s2c_r, s2c_w = os.pipe()
+
+    def start(ls: LanguageServer, fdr, fdw):
+        # TODO: better patch is needed
+        # disable `close()` to avoid error messages
+        close = ls.loop.close
+        ls.loop.close = lambda: None
+        ls.start_io(os.fdopen(fdr, 'rb'), os.fdopen(fdw, 'wb'))
+        ls.loop.close = close
+
+    server = CMakeLanguageServer(asyncio.new_event_loop())
+    server_thread = Thread(target=start, args=(server, c2s_r, s2c_w))
+    server_thread.start()
+
+    client = LanguageServer(asyncio.new_event_loop())
+    client_thread = Thread(target=start, args=(client, s2c_r, c2s_w))
+    client_thread.start()
+
+    yield client, server
+
+    client.send_notification(features.EXIT)
+    server.send_notification(features.EXIT)
+    server_thread.join()
+    client_thread.join()
diff --git a/tests/test_server.py b/tests/test_server.py
new file mode 100644
index 0000000..22863df
--- /dev/null
+++ b/tests/test_server.py
@@ -0,0 +1,130 @@
+from concurrent import futures
+from pathlib import Path
+from typing import Optional
+
+from pygls.features import (COMPLETION, FORMATTING, HOVER, INITIALIZE,
+                            TEXT_DOCUMENT_DID_OPEN)
+from pygls.server import LanguageServer
+from pygls.types import (CompletionContext, CompletionParams,
+                         CompletionTriggerKind, DidOpenTextDocumentParams,
+                         DocumentFormattingParams, FormattingOptions,
+                         InitializeParams, Position, TextDocumentIdentifier,
+                         TextDocumentItem, TextDocumentPositionParams)
+
+CALL_TIMEOUT = 2
+
+
+def _init(client: LanguageServer, root: Path):
+    retry = 3
+    while retry > 0:
+        try:
+            client.lsp.send_request(
+                INITIALIZE,
+                InitializeParams(
+                    process_id=1234, root_uri=root.as_uri(),
+                    capabilities=None)).result(timeout=CALL_TIMEOUT)
+        except futures.TimeoutError:
+            retry -= 1
+        else:
+            break
+
+
+def _open(client: LanguageServer, path: Path, text: Optional[str] = None):
+    if text is None:
+        with open(path) as fp:
+            text = fp.read()
+
+    client.lsp.notify(
+        TEXT_DOCUMENT_DID_OPEN,
+        DidOpenTextDocumentParams(
+            TextDocumentItem(path.as_uri(), 'cmake', 1, text)))
+
+
+def test_initialize(client_server, datadir):
+    client, server = client_server
+
+    assert server._api is None
+    _init(client, datadir)
+    assert server._api is not None
+
+
+def test_completions_invoked(client_server, datadir):
+    client, server = client_server
+    _init(client, datadir)
+    path = datadir / 'CMakeLists.txt'
+    _open(client, path, 'projec')
+    response = client.lsp.send_request(
+        COMPLETION,
+        CompletionParams(TextDocumentIdentifier(path.as_uri()), Position(
+            0, 6), CompletionContext(
+                CompletionTriggerKind.Invoked))).result(timeout=CALL_TIMEOUT)
+    item = next(filter(lambda x: x.label == 'project', response.items), None)
+    assert item is not None
+    assert '<PROJECT-NAME>' in item.documentation
+
+
+def test_completions_triggercharacter_variable(client_server, datadir):
+    client, server = client_server
+    _init(client, datadir)
+    path = datadir / 'CMakeLists.txt'
+    _open(client, path, '${')
+    response = client.lsp.send_request(
+        COMPLETION,
+        CompletionParams(
+            TextDocumentIdentifier(path.as_uri()), Position(0, 2),
+            CompletionContext(CompletionTriggerKind.TriggerCharacter,
+                              '{'))).result(timeout=CALL_TIMEOUT)
+    assert 'PROJECT_VERSION' in [x.label for x in response.items]
+
+
+def test_completions_triggercharacter_module(client_server, datadir):
+    client, server = client_server
+    _init(client, datadir)
+    path = datadir / 'CMakeLists.txt'
+    _open(client, path, 'include(')
+    response = client.lsp.send_request(
+        COMPLETION,
+        CompletionParams(
+            TextDocumentIdentifier(path.as_uri()), Position(0, 8),
+            CompletionContext(CompletionTriggerKind.TriggerCharacter,
+                              '('))).result(timeout=CALL_TIMEOUT)
+    assert 'GoogleTest' in [x.label for x in response.items]
+
+
+def test_completions_triggercharacter_package(client_server, datadir):
+    client, server = client_server
+    _init(client, datadir)
+    path = datadir / 'CMakeLists.txt'
+    _open(client, path, 'find_package(')
+    response = client.lsp.send_request(
+        COMPLETION,
+        CompletionParams(
+            TextDocumentIdentifier(path.as_uri()), Position(0, 13),
+            CompletionContext(CompletionTriggerKind.TriggerCharacter,
+                              '('))).result(timeout=CALL_TIMEOUT)
+    assert 'Boost' in [x.label for x in response.items]
+
+
+def test_formatting(client_server, datadir):
+    client, server = client_server
+    _init(client, datadir)
+    path = datadir / 'CMakeLists.txt'
+    _open(client, path, 'a ( b c ) ')
+    response = client.lsp.send_request(
+        FORMATTING,
+        DocumentFormattingParams(TextDocumentIdentifier(path.as_uri()),
+                                 FormattingOptions(
+                                     2, True))).result(timeout=CALL_TIMEOUT)
+    assert response[0].newText == 'a(b c)\n'
+
+
+def test_hover(client_server, datadir):
+    client, server = client_server
+    _init(client, datadir)
+    path = datadir / 'CMakeLists.txt'
+    _open(client, path, 'project()')
+    response = client.lsp.send_request(
+        HOVER,
+        TextDocumentPositionParams(TextDocumentIdentifier(path.as_uri()),
+                                   Position())).result(timeout=CALL_TIMEOUT)
+    assert '<PROJECT-NAME>' in response.contents.value
diff --git a/tox.ini b/tox.ini
index 027a718..ea9eb0a 100644
--- a/tox.ini
+++ b/tox.ini
@@ -16,7 +16,7 @@ passenv = INCLUDE LIB LIBPATH Platform VCTools* VSCMD_* WindowsSDK*
 commands_pre =
     poetry install
 commands =
-    poetry run pytest --cov-report=xml --cov=src -sv tests
+    poetry run pytest --cov-report=term --cov-report=xml --cov=src -sv tests
 
 [testenv:lint]
 commands =