Create a smoke test for test-infra (#138)

* Create a smoke test for test-infra

This will ensure the test infrastructure is not broken.

Fixes #7.

Bonus: remove the `dummy.go` file.

* Restrict unit tests to `/test`, as it's the only directory with tests

test/presubmit-tests.sh

@@ -36,7 +36,8 @@ function build_tests() {
 }
 
 function unit_tests() {
-  header "TODO(#7): Running unit tests"
+  header "Running unit tests"
+  report_go_test ./test/...
 }
 
 function integration_tests() {

test/smoke_test.go

@@ -0,0 +1,25 @@
+/*
+Copyright 2018 The Knative Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package smoke
+
+import (
+	"testing"
+)
+
+func TestTestingInfrastructureWorks(t *testing.T) {
+	// Always succeed.
+}