Add test for the new functionality

Author: toote

tests/run.bats

@@ -900,6 +900,29 @@ cmd3"
   unstub buildkite-agent
 }
 
+@test "Run with empty entrypoint" {
+  export BUILDKITE_PLUGIN_DOCKER_COMPOSE_RUN=myservice
+  export BUILDKITE_COMMAND=""
+  export BUILDKITE_PLUGIN_DOCKER_COMPOSE_CHECK_LINKED_CONTAINERS=false
+  export BUILDKITE_PLUGIN_DOCKER_COMPOSE_CLEANUP=false
+  export BUILDKITE_PLUGIN_DOCKER_COMPOSE_ENTRYPOINT=""
+
+  stub docker \
+    "compose -f docker-compose.yml -p buildkite1111 up -d --scale myservice=0 myservice : echo ran myservice dependencies" \
+    "compose -f docker-compose.yml -p buildkite1111 run --name buildkite1111_myservice_build_1 -T --rm --entrypoint '' myservice : echo ran myservice"
+
+  stub buildkite-agent \
+    "meta-data exists docker-compose-plugin-built-image-tag-myservice : exit 1"
+
+  run "$PWD"/hooks/command
+
+  assert_success
+  assert_output --partial "ran myservice"
+
+  unstub docker
+  unstub buildkite-agent
+}
+
 @test "Run with mount-buildkite-agent enabled" {
   export BUILDKITE_PLUGIN_DOCKER_COMPOSE_RUN=myservice
   export BUILDKITE_COMMAND=""