backport of commit 9d15017 (hashicorp#20460)

Co-authored-by: miagilepner <mia.epner@hashicorp.com>

Makefile

@@ -30,16 +30,16 @@ default: dev
 bin: prep
 	@CGO_ENABLED=$(CGO_ENABLED) BUILD_TAGS='$(BUILD_TAGS) ui' sh -c "'$(CURDIR)/scripts/build.sh'"
 
-testonly: 
-	$(eval BUILD_TAGS += testonly)
-
 # dev creates binaries for testing Vault locally. These are put
 # into ./bin/ as well as $GOPATH/bin
-dev: prep testonly
+dev: BUILD_TAGS+=testonly
+dev: prep
 	@CGO_ENABLED=$(CGO_ENABLED) BUILD_TAGS='$(BUILD_TAGS)' VAULT_DEV_BUILD=1 sh -c "'$(CURDIR)/scripts/build.sh'"
-dev-ui: assetcheck prep testonly
+dev-ui: BUILD_TAGS+=testonly
+dev-ui: assetcheck prep
 	@CGO_ENABLED=$(CGO_ENABLED) BUILD_TAGS='$(BUILD_TAGS) ui' VAULT_DEV_BUILD=1 sh -c "'$(CURDIR)/scripts/build.sh'"
-dev-dynamic: prep testonly
+dev-dynamic: BUILD_TAGS+=testonly
+dev-dynamic: prep
 	@CGO_ENABLED=1 BUILD_TAGS='$(BUILD_TAGS)' VAULT_DEV_BUILD=1 sh -c "'$(CURDIR)/scripts/build.sh'"
 
 # *-mem variants will enable memory profiling which will write snapshots of heap usage
@@ -54,36 +54,42 @@ dev-dynamic-mem: dev-dynamic
 
 # Creates a Docker image by adding the compiled linux/amd64 binary found in ./bin.
 # The resulting image is tagged "vault:dev".
-docker-dev: prep testonly
+docker-dev: BUILD_TAGS+=testonly
+docker-dev: prep
 	docker build --build-arg VERSION=$(GO_VERSION_MIN) --build-arg BUILD_TAGS="$(BUILD_TAGS)" -f scripts/docker/Dockerfile -t vault:dev .
 
-docker-dev-ui: prep testonly
+docker-dev-ui: BUILD_TAGS+=testonly
+docker-dev-ui: prep
 	docker build --build-arg VERSION=$(GO_VERSION_MIN) --build-arg BUILD_TAGS="$(BUILD_TAGS)" -f scripts/docker/Dockerfile.ui -t vault:dev-ui .
 
 # test runs the unit tests and vets the code
-test: prep testonly
+test: BUILD_TAGS+=testonly
+test: prep
 	@CGO_ENABLED=$(CGO_ENABLED) \
 	VAULT_ADDR= \
 	VAULT_TOKEN= \
 	VAULT_DEV_ROOT_TOKEN_ID= \
 	VAULT_ACC= \
 	$(GO_CMD) test -tags='$(BUILD_TAGS)' $(TEST) $(TESTARGS) -timeout=$(TEST_TIMEOUT) -parallel=20
 
-testcompile: prep testonly
+testcompile: BUILD_TAGS+=testonly
+testcompile: prep
 	@for pkg in $(TEST) ; do \
 		$(GO_CMD) test -v -c -tags='$(BUILD_TAGS)' $$pkg -parallel=4 ; \
 	done
 
 # testacc runs acceptance tests
-testacc: prep testonly
+testacc: BUILD_TAGS+=testonly
+testacc: prep
 	@if [ "$(TEST)" = "./..." ]; then \
 		echo "ERROR: Set TEST to a specific package"; \
 		exit 1; \
 	fi
 	VAULT_ACC=1 $(GO_CMD) test -tags='$(BUILD_TAGS)' $(TEST) -v $(TESTARGS) -timeout=$(EXTENDED_TEST_TIMEOUT)
 
 # testrace runs the race checker
-testrace: prep testonly
+testrace: BUILD_TAGS+=testonly
+testrace: prep
 	@CGO_ENABLED=1 \
 	VAULT_ADDR= \
 	VAULT_TOKEN= \