Parameterize service infra test code for container image tag

Using the latest commit hash should generally be correct, especially in
the CI environment, but there are situations where it's nice to be able
to specify which version of the service to deploy.

Also extract out the environment name being used, for code clarity.

Author: doshitan

Makefile

@@ -272,7 +272,7 @@ infra-format: ## Format infra code
 
 infra-test-service: ## Run service layer infra test suite
 	@:$(call check_defined, APP_NAME, "the name of subdirectory of /infra that holds the application's infrastructure code")
-	cd infra/test && APP_NAME=$(APP_NAME) go test -run TestService -v -timeout 30m
+	cd infra/test && APP_NAME=$(APP_NAME) IMAGE_TAG=$(IMAGE_TAG) go test -run TestService -v -timeout 30m
 
 #############
 ## Linting ##

infra/test/infra_test.go

@@ -23,24 +23,21 @@ import (
 var uniqueId = strings.ToLower(generateTestId())
 var workspaceName = fmt.Sprintf("t-%s", uniqueId)
 var testAppName = os.Getenv("APP_NAME")
+var imageTag = os.Getenv("IMAGE_TAG")
+var environmentName = "dev"
 
 func TestService(t *testing.T) {
-	imageTag := shell.RunCommandAndGetOutput(t, shell.Command{
-		Command:    "git",
-		Args:       []string{"rev-parse", "HEAD"},
-		WorkingDir: "./",
-	})
 	terraformOptions := terraform.WithDefaultRetryableErrors(t, &terraform.Options{
 		Reconfigure:  true,
 		TerraformDir: fmt.Sprintf("../%s/service/", testAppName),
 		Vars: map[string]interface{}{
-			"environment_name": "dev",
+			"environment_name": environmentName,
 			"image_tag":        imageTag,
 		},
 	})
 
 	fmt.Println("::group::Initialize service module")
-	TerraformInit(t, terraformOptions, "dev.s3.tfbackend")
+	TerraformInit(t, terraformOptions, fmt.Sprintf("%s.s3.tfbackend", environmentName))
 	fmt.Println("::endgroup::")
 
 	defer terraform.WorkspaceDelete(t, terraformOptions, workspaceName)
@@ -60,7 +57,6 @@ func TestService(t *testing.T) {
 func WaitForServiceToBeStable(t *testing.T, workspaceName string) {
 	fmt.Println("::group::Wait for service to be stable")
 	appName := testAppName
-	environmentName := "dev"
 	serviceName := fmt.Sprintf("%s-%s-%s", workspaceName, appName, environmentName)
 	shell.RunCommand(t, shell.Command{
 		Command:    "aws",