cmd/snap, tests: add some snap download tests

from the unit tests,

    // these only cover errors that happen before hitting the network,
    // because we're not (yet!) mocking the tooling store

so it checks for bad combinations (multiple channels,
revision+channel, revision+cohort).

and in spread tests, check for the 'invalid cohort key' error.

cmd/snap/cmd_download_test.go

@@ -0,0 +1,53 @@
+// -*- Mode: Go; indent-tabs-mode: t -*-
+
+/*
+ * Copyright (C) 2019 Canonical Ltd
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+package main_test
+
+import (
+	"gopkg.in/check.v1"
+
+	snap "github.com/snapcore/snapd/cmd/snap"
+)
+
+// these only cover errors that happen before hitting the network,
+// because we're not (yet!) mocking the tooling store
+
+func (s *SnapSuite) TestDownloadBadChannelCombo(c *check.C) {
+	_, err := snap.Parser(snap.Client()).ParseArgs([]string{
+		"download", "--beta", "--channel=foo", "a-snap",
+	})
+
+	c.Check(err, check.ErrorMatches, "Please specify a single channel")
+}
+
+func (s *SnapSuite) TestDownloadCohortAndRevision(c *check.C) {
+	_, err := snap.Parser(snap.Client()).ParseArgs([]string{
+		"download", "--cohort=what", "--revision=1234", "a-snap",
+	})
+
+	c.Check(err, check.ErrorMatches, "cannot specify both cohort and revision")
+}
+
+func (s *SnapSuite) TestDownloadChannelAndRevision(c *check.C) {
+	_, err := snap.Parser(snap.Client()).ParseArgs([]string{
+		"download", "--beta", "--revision=1234", "a-snap",
+	})
+
+	c.Check(err, check.ErrorMatches, "cannot specify both channel and revision")
+}

cmd/snap/cmd_run_test.go

@@ -52,13 +52,13 @@ hooks:
 
 type RunSuite struct {
 	fakeHome string
-	SnapSuite
+	BaseSnapSuite
 }
 
 var _ = check.Suite(&RunSuite{})
 
 func (s *RunSuite) SetUpTest(c *check.C) {
-	s.SnapSuite.SetUpTest(c)
+	s.BaseSnapSuite.SetUpTest(c)
 	s.fakeHome = c.MkDir()
 
 	u, err := user.Current()

tests/main/snap-download/task.yaml

@@ -39,3 +39,9 @@ execute: |
     snap download --cohort="MSBlRmU4QlRSNUw1VjlGN3lIZU1BUHhrRXIyTmRVWE10dyAxNTU1NTE0MzA5IDg3ZmUwMjhkZDFjMTQ1MDY5N2QyZjdiMGZkMzgzODk0NjMzMmFhOTZmZmFjZmFlNmU2MGQyOTNjYzE1OTE3NWY=" test-snapd-tools
     ls test-snapd-tools_*.snap
     verify_asserts test-snapd-tools_*.assert
+    rm -v test-snapd-tools*
+
+    echo "Can't ask for invalid cohort"
+    ! snap download --cohort="what" test-snapd-tools 2>out
+    MATCH 'cannot download snap.*: Invalid cohort key' < out
+