Shed diff enhancements.

 - Add test case.
 - Add option to write diff out to a file (needed for test, but good functionality on its own).
 - Improved labelling when using full URLs to tool sheds.

planemo/commands/cmd_shed_diff.py

@@ -17,6 +17,12 @@
 @options.shed_owner_option()
 @options.shed_name_option()
 @options.shed_target_option()
+@click.option(
+    "-o", "--output",
+    type=click.Path(file_okay=True, resolve_path=True),
+    help="Send diff output to specified file.",
+    default=None,
+)
 @click.option(
     '--shed_target_source',
     help="Source Tool Shed to diff against (will ignore local project info"
@@ -55,7 +61,10 @@ def diff_in(ctx, working, path, **kwds):
     shed_target_source = kwds.get("shed_target_source", None)
 
     label_a = "_%s_" % (shed_target_source if shed_target_source else "local")
-    label_b = "_%s_" % kwds.get("shed_target", "B")
+    shed_target = kwds.get("shed_target", "B")
+    if "/" in shed_target:
+        shed_target = "custom_shed"
+    label_b = "_%s_" % shed_target
 
     mine = os.path.join(working, label_a)
     other = os.path.join(working, label_b)
@@ -87,4 +96,7 @@ def diff_in(ctx, working, path, **kwds):
         cmd_template = 'mkdir "%s"; tar -xzf "%s" -C "%s"; rm -rf %s'
         shell(cmd_template % (mine, tar_path, mine, tar_path))
 
-    shell('cd "%s"; diff -r %s %s' % (working, label_a, label_b))
+    cmd = 'cd "%s"; diff -r %s %s' % (working, label_a, label_b)
+    if kwds["output"]:
+        cmd += "> '%s'" % kwds["output"]
+    shell(cmd)

tests/test_shed_diff.py

@@ -0,0 +1,30 @@
+""" Integration tests for shed_diff command.
+"""
+
+import os
+from .test_utils import CliShedTestCase
+
+DIFF_LINES = [
+    "diff -r _local_/related_file _custom_shed_/related_file",
+    "< A related non-tool file (modified).",
+    "> A related non-tool file.",
+]
+
+
+class ShedUploadTestCase(CliShedTestCase):
+
+    def test_shed_diff(self):
+        with self._isolate_repo("single_tool") as f:
+            upload_command = ["shed_upload", "--force_repository_creation"]
+            upload_command.extend(self._shed_args())
+            self._check_exit_code(upload_command)
+            with open(os.path.join(f, "related_file"), "w") as r_f:
+                r_f.write("A related non-tool file (modified).\n")
+
+            diff_command = ["shed_diff", "-o", "diff"]
+            diff_command.extend(self._shed_args(read_only=True))
+            self._check_exit_code(diff_command)
+            with open("diff", "r") as f:
+                diff = f.read()
+            for diff_line in DIFF_LINES:
+                assert diff_line in diff