Add test and documentation for running envkernel recursively

- This does not intrinsically add anything new to envkernel, this
  already worked.  But see the commits right before this for some
  necessary fixes that had to be made in order to do this.
- Add one basic test, which runs lmod and then conda and checks that
  the internal invocation has the same arguments as the first kernel.
- Otherwise, this is still quite untested (I haven't even run it
  myself, beyond this one artifical test...)

Author: rkdarst

README.md

@@ -336,6 +336,28 @@ envkernel parses and manipulates these arguments however is needed.
 
 
 
+## Running multiple modes
+
+envkernel doesn't support running multiple modes - for example,
+`conda` and `lmod` at the same time.  But, because of the general
+nature, you should be able to layer it yourself.  The following
+example uses the `conda` mode to create an envkernel.  Then, it uses
+`--kernel-template` to re-read that kernel and wrap it in `lmod`:
+
+```
+envkernel conda --name=test1 conda_path
+envkernel lmod --name=test1 --kernel-template=test1 lmod_module
+```
+
+There is nothing really special here, it is layering one envkernel
+execution on top of another.  If you notice problems with this, please
+try to debug a bit and then send feedback/improvements, this is a
+relatively new feature.
+
+
+
+
+
 ## Use with nbgrader
 
 envkernel was orginally inspired by the need for nbgrader to securely

test_envkernel.py

@@ -163,6 +163,31 @@ def test_env(d, mode):
     assert kern['kernel']['env']['CCC'] == 'DDD'
 
 
+def test_recursive_run(d):
+    """Test envkernel being called on itself.
+
+    Roughly runs this, which :
+
+    envkernel lmod --name=test1 LMOD
+    envkernel conda --kernel-template=test1 --name=test1 CPATH
+    """
+    # Must set JUPYTER_PATH to be able to load the new kernel template
+    os.environ['JUPYTER_PATH'] = pjoin(d, 'share/jupyter')
+    kern1 = install(d, "lmod LMOD", name='test1')
+    #print(kern1['kernel']['argv'])
+    # Test the conda install
+    CPATH = pjoin(d, 'test-conda')
+    os.mkdir(CPATH)
+    os.mkdir(pjoin(CPATH, 'bin'))
+    kern2 = install(d, "conda --kernel-template=test1 %s"%CPATH, name='test1')
+    #print(kern2['kernel']['argv'])
+    def test_exec(_file, _args):
+        #print(kern1['kernel']['argv'])
+        # Exclude the last argument, which is the connection file
+        assert _args[:-1] == kern1['kernel']['argv'][:-1]
+    run(d, kern2, test_exec)
+
+
 
 # Languages
 @all_modes()