diff --git a/setup.py b/setup.py
index f4ebee0c..f5eca1fc 100644
--- a/setup.py
+++ b/setup.py
@@ -20,6 +20,7 @@
 
 tests_require = [
     'pytest',
+    'pytest_timeout',
 ]
 
 extras_require = {
diff --git a/test/test_attach.py b/test/test_attach.py
new file mode 100644
index 00000000..c1588ca0
--- /dev/null
+++ b/test/test_attach.py
@@ -0,0 +1,137 @@
+"""Tests other session_types than subprocess Nvim."""
+
+import contextlib
+import os.path
+import socket
+import subprocess
+import tempfile
+import time
+from typing import Generator
+
+import pytest
+import pytest_timeout  # pylint: disable=unused-import  # noqa
+
+import pynvim
+from pynvim.api import Nvim
+
+# pylint: disable=consider-using-with
+# pylint: disable=redefined-outer-name
+
+
+xfail_on_windows = pytest.mark.xfail(
+    "os.name == 'nt'", reason="Broken in Windows, see #544")
+
+
+@pytest.fixture
+def tmp_socket() -> Generator[str, None, None]:
+    """Get a temporary UNIX socket file."""
+    # see cpython#93914
+    addr = tempfile.mktemp(prefix="test_python_", suffix='.sock',
+                           dir=os.path.curdir)
+    try:
+        yield addr
+    finally:
+        if os.path.exists(addr):
+            with contextlib.suppress(OSError):
+                os.unlink(addr)
+
+
+@xfail_on_windows
+def test_connect_socket(tmp_socket: str) -> None:
+    """Tests UNIX socket connection."""
+    p = subprocess.Popen(["nvim", "--clean", "-n", "--headless",
+                          "--listen", tmp_socket])
+    time.sleep(0.2)  # wait a bit until nvim starts up
+
+    try:
+        nvim: Nvim = pynvim.attach('socket', path=tmp_socket)
+        assert 42 == nvim.eval('42')
+        assert "?" == nvim.command_output('echo "?"')
+    finally:
+        with contextlib.suppress(OSError):
+            p.terminate()
+
+
+def test_connect_socket_fail() -> None:
+    """Tests UNIX socket connection, when the sock file is not found."""
+    with pytest.raises(FileNotFoundError):
+        pynvim.attach('socket', path='/tmp/not-exist.socket')
+
+
+def find_free_port() -> int:
+    """Find a free, available port number."""
+    with socket.socket() as sock:
+        sock.bind(('', 0))  # Bind to a free port provided by the host.
+        return sock.getsockname()[1]
+
+
+def test_connect_tcp() -> None:
+    """Tests TCP connection."""
+    address = '127.0.0.1'
+    port = find_free_port()
+    p = subprocess.Popen(["nvim", "--clean", "-n", "--headless",
+                          "--listen", f"{address}:{port}"])
+    time.sleep(0.2)  # wait a bit until nvim starts up
+
+    try:
+        nvim: Nvim = pynvim.attach('tcp', address=address, port=port)
+        assert 42 == nvim.eval('42')
+        assert "?" == nvim.command_output('echo "?"')
+    finally:
+        with contextlib.suppress(OSError):
+            p.terminate()
+
+
+@pytest.mark.timeout(5.0)
+def test_connect_tcp_no_server() -> None:
+    """Tests TCP socket connection that fails; connection refused."""
+    port = find_free_port()
+
+    with pytest.raises(ConnectionRefusedError):
+        pynvim.attach('tcp', address='127.0.0.1', port=port)
+
+
+@xfail_on_windows
+def test_connect_stdio(vim: Nvim) -> None:
+    """Tests stdio connection, using jobstart(..., {'rpc': v:true})."""
+
+    def source(vim: Nvim, code: str) -> None:
+        """Source a vimscript code in the embedded nvim instance."""
+        fd, fname = tempfile.mkstemp()
+        try:
+            with os.fdopen(fd, 'w') as f:
+                f.write(code)
+            vim.command('source ' + fname)
+        finally:
+            os.unlink(fname)
+
+    # A helper function for debugging that captures what pynvim writes to
+    # stderr (e.g. python stacktrace): used as a |on_stderr| callback
+    source(vim, """
+        function! OutputHandler(j, lines, event_type)
+            if a:event_type == 'stderr'
+                for l:line in a:lines
+                    echom l:line
+                endfor
+            endif
+        endfunction
+    """)
+
+    remote_py_code = '\n'.join([
+        'import pynvim',
+        'nvim = pynvim.attach("stdio")',
+        'print("rplugins can write to stdout")',  # tests #377 (#60)
+        'nvim.api.command("let g:success = 42")',
+    ])
+    # see :help jobstart(), *jobstart-options* |msgpack-rpc|
+    jobid = vim.funcs.jobstart([
+        'python', '-c', remote_py_code,
+    ], {'rpc': True, 'on_stderr': 'OutputHandler'})
+    assert jobid > 0
+    exitcode = vim.funcs.jobwait([jobid], 500)[0]
+    messages = vim.command_output('messages')
+    assert exitcode == 0, ("the python process failed, :messages =>\n\n" +
+                           messages)
+
+    assert 42 == vim.eval('g:success')
+    assert "rplugins can write to stdout" in messages
diff --git a/test/test_vim.py b/test/test_vim.py
index 1c12e26e..58e305a3 100644
--- a/test/test_vim.py
+++ b/test/test_vim.py
@@ -1,3 +1,5 @@
+"""Tests interaction with neovim via Nvim API (with child process)."""
+
 import os
 import sys
 import tempfile