diff --git a/bin/run_tests.py b/bin/run_tests.py
index 117f8b9f..1a1895cf 100755
--- a/bin/run_tests.py
+++ b/bin/run_tests.py
@@ -10,7 +10,7 @@ if __name__ == '__main__':
     os.chdir(Path(__file__).resolve().parents[1])
 
     # run the unit tests
-    subprocess.check_call([sys.executable, '-m', 'pytest', 'unit_test'])
+    subprocess.check_call([sys.executable, '-m', 'pytest', 'unit_test', '--runslow'])
 
     # run the integration tests
     subprocess.check_call([sys.executable, '-m', 'pytest', '-x', '--durations', '0', 'test'])
diff --git a/unit_test/conftest.py b/unit_test/conftest.py
new file mode 100644
index 00000000..e446d0a1
--- /dev/null
+++ b/unit_test/conftest.py
@@ -0,0 +1,21 @@
+import pytest
+
+
+def pytest_addoption(parser):
+    parser.addoption(
+        "--runslow", action="store_true", default=False, help="run slow tests"
+    )
+
+
+def pytest_configure(config):
+    config.addinivalue_line("markers", "slow: mark test as slow to run")
+
+
+def pytest_collection_modifyitems(config, items):
+    if config.getoption("--runslow"):
+        # --runslow given in cli: do not skip slow tests
+        return
+    skip_slow = pytest.mark.skip(reason="need --runslow option to run")
+    for item in items:
+        if "slow" in item.keywords:
+            item.add_marker(skip_slow)
diff --git a/unit_test/docker_container_test.py b/unit_test/docker_container_test.py
new file mode 100644
index 00000000..e8ddc7d1
--- /dev/null
+++ b/unit_test/docker_container_test.py
@@ -0,0 +1,85 @@
+import pytest
+from cibuildwheel.docker_container import DockerContainer
+import subprocess
+import time
+import textwrap
+
+DEFAULT_IMAGE = 'centos:6'
+
+@pytest.mark.slow
+def test_simple():
+    with DockerContainer(DEFAULT_IMAGE) as container:
+        assert container.call(['echo', 'hello'], capture_output=True) == 'hello\n'
+
+@pytest.mark.slow
+def test_no_lf():
+    with DockerContainer(DEFAULT_IMAGE) as container:
+        assert container.call(['printf', 'hello'], capture_output=True) == 'hello'
+
+@pytest.mark.slow
+def test_environment():
+    with DockerContainer(DEFAULT_IMAGE) as container:
+        assert container.call(['sh', '-c', 'echo $TEST_VAR'], env={'TEST_VAR': '1'}, capture_output=True) == '1\n'
+
+@pytest.mark.slow
+def test_container_removed():
+    start_time = time.time()
+    with DockerContainer(DEFAULT_IMAGE) as container:
+        container.call(['true'])
+        docker_containers_listing = subprocess.run('docker container ls', shell=True, check=True, capture_output=True, universal_newlines=True).stdout
+        assert container.name in docker_containers_listing
+        old_container_name = container.name
+
+    docker_containers_listing = subprocess.run('docker container ls', shell=True, check=True, capture_output=True, universal_newlines=True).stdout
+    assert old_container_name not in docker_containers_listing
+
+@pytest.mark.slow
+def test_large_environment():
+    # max environment variable size is 128kB
+    long_env_var_length = 127*1024
+    large_environment = {
+        'a': '0'*long_env_var_length,
+        'b': '0'*long_env_var_length,
+        'c': '0'*long_env_var_length,
+        'd': '0'*long_env_var_length,
+    }
+
+    with DockerContainer(DEFAULT_IMAGE) as container:
+        # check the length of d
+        assert container.call(['sh', '-c', 'echo ${#d}'], env=large_environment, capture_output=True) == f'{long_env_var_length}\n'
+
+@pytest.mark.slow
+def test_binary_output():
+    with DockerContainer(DEFAULT_IMAGE) as container:
+        # the centos image only has python 2.6, so the below embedded snippets
+        # are in python2
+
+        # check that we can pass though arbitrary binary data without erroring
+        container.call(['/usr/bin/python2', '-c', textwrap.dedent('''
+            import sys
+            sys.stdout.write(''.join(chr(n) for n in range(0, 256)))
+        ''')])
+
+        # check that we can capture arbitrary binary data
+        output = container.call(['/usr/bin/python2', '-c', textwrap.dedent('''
+            import sys
+            sys.stdout.write(''.join(chr(n % 256) for n in range(0, 512)))
+        ''')], capture_output=True)
+
+        data = bytes(output, encoding='utf8', errors='surrogateescape')
+
+        for i in range(0, 512):
+            assert data[i] == i % 256
+
+        # check that environment variables can carry binary data, except null characters
+        # (https://www.gnu.org/software/libc/manual/html_node/Environment-Variables.html)
+        binary_data = bytes(n for n in range(1, 256))
+        binary_data_string = str(binary_data, encoding='utf8', errors='surrogateescape')
+        output = container.call(
+            ['python2', '-c', 'import os, sys; sys.stdout.write(os.environ["TEST_VAR"])'],
+            env={'TEST_VAR': binary_data_string},
+            capture_output=True,
+        )
+        assert output == binary_data_string
+
+