Add some simple e2e tests for executing CLI plugins

To help with this add a bad plugin which produces invalid metadata and arrange
for it to be built in the e2e container.

Signed-off-by: Ian Campbell <ijc@docker.com>

e2e/cli-plugins/run_test.go

@@ -0,0 +1,60 @@
+package cliplugins
+
+import (
+	"testing"
+
+	"gotest.tools/assert"
+	is "gotest.tools/assert/cmp"
+	"gotest.tools/golden"
+	"gotest.tools/icmd"
+)
+
+// TestRunNonexisting ensures correct behaviour when running a nonexistent plugin.
+func TestRunNonexisting(t *testing.T) {
+	run, cleanup := prepare(t)
+	defer cleanup()
+
+	res := icmd.RunCmd(run("nonexistent"))
+	res.Assert(t, icmd.Expected{
+		ExitCode: 1,
+	})
+	assert.Assert(t, is.Equal(res.Stdout(), ""))
+	golden.Assert(t, res.Stderr(), "docker-nonexistent-err.golden")
+}
+
+// TestRunBad ensures correct behaviour when running an existent but invalid plugin
+func TestRunBad(t *testing.T) {
+	run, cleanup := prepare(t)
+	defer cleanup()
+
+	res := icmd.RunCmd(run("badmeta"))
+	res.Assert(t, icmd.Expected{
+		ExitCode: 1,
+	})
+	assert.Assert(t, is.Equal(res.Stdout(), ""))
+	golden.Assert(t, res.Stderr(), "docker-badmeta-err.golden")
+}
+
+// TestRunGood ensures correct behaviour when running a valid plugin
+func TestRunGood(t *testing.T) {
+	run, cleanup := prepare(t)
+	defer cleanup()
+
+	res := icmd.RunCmd(run("helloworld"))
+	res.Assert(t, icmd.Expected{
+		ExitCode: 0,
+		Out:      "Hello World!",
+	})
+}
+
+// TestRunGoodSubcommand ensures correct behaviour when running a valid plugin with a subcommand
+func TestRunGoodSubcommand(t *testing.T) {
+	run, cleanup := prepare(t)
+	defer cleanup()
+
+	res := icmd.RunCmd(run("helloworld", "goodbye"))
+	res.Assert(t, icmd.Expected{
+		ExitCode: 0,
+		Out:      "Goodbye World!",
+	})
+}