Support transcrypt (#197)

Support is inherently provided by `enter`, which supports a command.
I've added a `transcrypt` command, which is really just an alias
under-the-hood for "enter transcrypt".

test/conftest.py

@@ -96,6 +96,7 @@ def supported_commands():
         'introspect',
         'list',
         'perms',
+        'transcrypt',
         'upgrade',
         'version',
         ]

test/test_ext_crypt.py

@@ -1,4 +1,4 @@
-"""Test git-crypt"""
+"""Test external encryption commands"""
 
 import pytest
 
@@ -8,15 +8,21 @@ import pytest
     [False, 'installed', 'installed-but-failed'],
     ids=['not-installed', 'installed', 'installed-but-failed']
 )
-def test_git_crypt(runner, yadm, paths, tmpdir, crypt):
-    """git-crypt tests"""
+@pytest.mark.parametrize(
+        'cmd,var', [
+            ['git_crypt', 'GIT_CRYPT_PROGRAM'],
+            ['transcrypt', 'TRANSCRYPT_PROGRAM'],
+        ],
+        ids=['git-crypt', 'transcrypt'])
+def test_ext_encryption(runner, yadm, paths, tmpdir, crypt, cmd, var):
+    """External encryption tests"""
 
     paths.repo.ensure(dir=True)
     bindir = tmpdir.mkdir('bin')
-    pgm = bindir.join('test-git-crypt')
+    pgm = bindir.join('test-ext-crypt')
 
     if crypt:
-        pgm.write(f'#!/bin/sh\necho git-crypt ran\n')
+        pgm.write(f'#!/bin/sh\necho ext-crypt ran\n')
         pgm.chmod(0o775)
     if crypt == 'installed-but-failed':
         pgm.write('false\n', mode='a')
@@ -24,8 +30,8 @@ def test_git_crypt(runner, yadm, paths, tmpdir, crypt):
     script = f"""
         YADM_TEST=1 source {yadm}
         YADM_REPO={paths.repo}
-        GIT_CRYPT_PROGRAM="{pgm}"
-        git_crypt "param1"
+        {var}="{pgm}"
+        {cmd} "param1"
     """
 
     run = runner(command=['bash'], inp=script)
@@ -35,7 +41,7 @@ def test_git_crypt(runner, yadm, paths, tmpdir, crypt):
             assert run.failure
         else:
             assert run.success
-        assert run.out.strip() == 'git-crypt ran'
+        assert run.out.strip() == 'ext-crypt ran'
     else:
         assert run.failure
         assert f"command '{pgm}' cannot be located" in run.out