`make test-docker` (#6059)

* Implement the test-docker make target

Running tests within docker allows us to resource constrain them better to not take over our systems. Additionally it allows us to run the tests on linux instead of the host OS which often times is macOS.

* Use GOMAXPROCS instead of -p

* Add a comment about docker cpus

GNUmakefile

@@ -19,6 +19,7 @@ endif
 GOOS?=$(shell go env GOOS)
 GOARCH?=$(shell go env GOARCH)
 GOPATH=$(shell go env GOPATH)
+MAIN_GOPATH=$(shell go env GOPATH | cut -d: -f1)
 
 ASSETFS_PATH?=agent/bindata_assetfs.go
 # Get the git commit
@@ -47,6 +48,30 @@ UI_BUILD_TAG?=consul-build-ui
 BUILD_CONTAINER_NAME?=consul-builder
 CONSUL_IMAGE_VERSION?=latest
 
+TEST_MODCACHE?=1
+TEST_BUILDCACHE?=1
+
+# You can only use as many CPUs as you have allocated to docker
+ifdef TEST_DOCKER_CPUS
+TEST_DOCKER_RESOURCE_CONSTRAINTS=--cpus $(TEST_DOCKER_CPUS)
+TEST_PARALLELIZATION=-e GOMAXPROCS=$(TEST_DOCKER_CPUS)
+else
+TEST_DOCKER_RESOURCE_CONSTRAINTS=
+TEST_PARALLELIZATION=
+endif
+
+ifeq ($(TEST_MODCACHE), 1)
+TEST_MODCACHE_VOL=-v $(MAIN_GOPATH)/pkg/mod:/go/pkg/mod
+else
+TEST_MODCACHE_VOL=
+endif
+
+ifeq ($(TEST_BUILDCACHE), 1)
+TEST_BUILDCACHE_VOL=-v $(shell go env GOCACHE):/root/.caches/go-build
+else
+TEST_BUILDCACHE_VOL=
+endif
+
 DIST_TAG?=1
 DIST_BUILD?=1
 DIST_SIGN?=1
@@ -211,6 +236,34 @@ test-ci: other-consul dev-build vet test-install-deps
 test-flake: other-consul vet test-install-deps
 	@$(SHELL) $(CURDIR)/build-support/scripts/test-flake.sh --pkg "$(FLAKE_PKG)" --test "$(FLAKE_TEST)" --cpus "$(FLAKE_CPUS)" --n "$(FLAKE_N)"
 
+test-docker: linux go-build-image
+	@# -ti run in the foreground showing stdout
+	@# --rm removes the container once its finished running
+	@# GO_MODCACHE_VOL - args for mapping in the go module cache
+	@# GO_BUILD_CACHE_VOL - args for mapping in the go build cache
+	@# All the env vars are so we pass through all the relevant bits of information
+	@# Needed for running the tests
+	@# We map in our local linux_amd64 bin directory as thats where the linux dep
+	@#   target dropped the binary. We could build the binary in the container too
+	@#   but that might take longer as caching gets weird
+	@# Lastly we map the source dir here to the /consul workdir
+	@echo "Running tests within a docker container"
+	@docker run -ti --rm \
+		-e 'GOTEST_FLAGS=$(GOTEST_FLAGS)' \
+		-e 'GOTEST_PKGS=$(GOTEST_PKGS)' \
+		-e 'GOTAGS=$(GOTAGS)' \
+		-e 'GIT_COMMIT=$(GIT_COMMIT)' \
+		-e 'GIT_DIRTY=$(GIT_DIRTY)' \
+		-e 'GIT_DESCRIBE=$(GIT_DESCRIBE)' \
+		$(TEST_PARALLELIZATION) \
+		$(TEST_DOCKER_RESOURCE_CONSTRAINTS) \
+		$(TEST_MODCACHE_VOL) \
+		$(TEST_BUILDCACHE_VOL) \
+		-v $(MAIN_GOPATH)/bin/linux_amd64/:/go/bin \
+		-v $(shell pwd):/consul \
+		$(GO_BUILD_TAG) \
+		make test-internal
+
 other-consul:
 	@echo "--> Checking for other consul instances"
 	@if ps -ef | grep 'consul agent' | grep -v grep ; then \