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>

runner/storage_test.go

@@ -2,6 +2,7 @@ package runner
 
 import (
 	"github.com/stretchr/testify/suite"
+	"gitlab.hpi.de/codeocean/codemoon/poseidon/api/dto"
 	"gitlab.hpi.de/codeocean/codemoon/poseidon/tests"
 	"testing"
 )
@@ -19,6 +20,7 @@ type RunnerPoolTestSuite struct {
 func (suite *RunnerPoolTestSuite) SetupTest() {
 	suite.runnerStorage = NewLocalRunnerStorage()
 	suite.runner = NewRunner(tests.DefaultRunnerId)
+	suite.runner.Add(tests.DefaultExecutionId, &dto.ExecutionRequest{Command: "true"})
 }
 
 func (suite *RunnerPoolTestSuite) TestAddedRunnerCanBeRetrieved() {