Add tests and end-to-end tests for websocket execution

For unit tests, this mocks the runners Execute method with a
customizable function that operates on the request, streams and exit
channel to simulate a real execution.

End-to-end tests are moved to the tests/e2e_tests folder. The tests
folder allows us to have shared helper functions for all tests in a
separate package (tests) that is not included in the non-test build.

This also adds one second of delay before each end-to-end test case by
using the TestSetup method of suite. By slowing down test execution,
this gives Nomad time to create new allocations when a test requested a
runner. Another solution could be to increase the scale of the job to
have enough allocations for all end-to-end tests.

Co-authored-by: Maximilian Paß <maximilian.pass@student.hpi.uni-potsdam.de>

tests/e2e/e2e_test.go

@@ -0,0 +1,44 @@
+package e2e
+
+import (
+	"github.com/stretchr/testify/suite"
+	"gitlab.hpi.de/codeocean/codemoon/poseidon/config"
+	"gitlab.hpi.de/codeocean/codemoon/poseidon/logging"
+	"os"
+	"testing"
+	"time"
+)
+
+/*
+* # E2E Tests
+*
+* For the e2e tests a nomad cluster must be connected and poseidon must be running.
+ */
+
+var log = logging.GetLogger("e2e")
+
+type E2ETestSuite struct {
+	suite.Suite
+}
+
+func (suite *E2ETestSuite) SetupTest() {
+	// Waiting one second before each test allows Nomad to rescale after tests requested runners.
+	<-time.After(time.Second)
+}
+
+func TestE2ETestSuite(t *testing.T) {
+	suite.Run(t, new(E2ETestSuite))
+}
+
+// Overwrite TestMain for custom setup.
+func TestMain(m *testing.M) {
+	log.Info("Test Setup")
+	err := config.InitConfig()
+	if err != nil {
+		log.Warn("Could not initialize configuration")
+	}
+	// ToDo: Add Nomad job here when it is possible to create execution environments. See #26.
+	log.Info("Test Run")
+	code := m.Run()
+	os.Exit(code)
+}