add unit tests for binder dir

Author: Joseph Hamman

repo2docker/__main__.py

@@ -7,6 +7,7 @@
 from . import __version__
 from .utils import validate_and_generate_port_mapping, is_valid_docker_image_name
 
+
 def validate_image_name(image_name):
     """
     Validate image_name read by argparse

tests/unit/test_binder_dir.py

@@ -0,0 +1,31 @@
+import os
+
+import pytest
+
+from repo2docker import buildpacks
+
+
+@pytest.mark.parametrize("binder_dir", ['.binder', 'binder'])
+def test_binder_dir_property(tmpdir, binder_dir):
+    tmpdir.chdir()
+    os.mkdir(binder_dir)
+
+    bp = buildpacks.BuildPack()
+    assert binder_dir in bp.binder_dir
+    assert bp.binder_path('foo.yaml') == os.path.join(binder_dir, 'foo.yaml')
+
+
+def test_root_binder_dir(tmpdir):
+    tmpdir.chdir()
+    bp = buildpacks.BuildPack()
+    assert bp.binder_dir == ''
+
+
+def test_exclusive_binder_dir(tmpdir):
+    tmpdir.chdir()
+    os.mkdir('./binder')
+    os.mkdir('./.binder')
+
+    bp = buildpacks.BuildPack()
+    with pytest.raises(RuntimeError):
+        _ = bp.binder_dir