Add unit test for conda environment management

- Also fix a bug caught by unit test!

tests/test_conda.py

@@ -0,0 +1,53 @@
+"""
+Test conda commandline wrappers
+"""
+from tljh import conda
+import os
+import pytest
+import subprocess
+import tempfile
+
+
+@pytest.fixture
+def prefix():
+    """
+    Provide a temporary directory to make environments in.
+    """
+    with tempfile.TemporaryDirectory() as tmpdir:
+        yield tmpdir
+
+
+def test_create_environment(prefix):
+    """
+    Test conda environment creation
+
+    An empty conda environment doesn't seem to have anything in it,
+    so we just check for directory existence.
+    """
+    conda.ensure_conda_env(prefix)
+    assert os.path.exists(prefix)
+
+
+def test_ensure_environment(prefix):
+    """
+    Test second call to ensure_conda_env works as expected
+
+    A conda environment already exists, so we it should just do nothing
+    """
+    conda.ensure_conda_env(prefix)
+    assert os.path.exists(prefix)
+    conda.ensure_conda_env(prefix)
+
+
+def test_ensure_packages(prefix):
+    """
+    Test installing packages in conda environment
+    """
+    conda.ensure_conda_env(prefix)
+    conda.ensure_conda_packages(prefix, ['numpy'])
+    # Throws an error if this fails
+    subprocess.check_call([
+        os.path.join(prefix, 'bin', 'python'),
+        '-c',
+        'import numpy'
+    ])