documenting test for #10301

enable -race detector for testing api

.circleci/config.yml

@@ -293,11 +293,15 @@ jobs:
       goarch:
         type: string
         default: "amd64"
+      enable_race_testing:
+        type: string
+        default: ""
     environment:
       GOTEST_PKGS_EXCLUDE: "<< parameters.exclude_packages >>"
       GOTEST_PKGS: "<< parameters.test_packages >>"
       GOTEST_MOD: "<< parameters.test_module >>"
       GOTESTARCH: "<< parameters.goarch >>"
+      ENABLE_RACE: "<< parameters.enable_race_testing >>"
     steps:
       - checkout
       - install-golang
@@ -616,6 +620,7 @@ workflows:
           name: "test-api"
           test_module: "api"
           filters: *backend_test_branches_filter
+          enable_race_testing: "1"
       - test-container:
           name: "test-devices"
           test_packages: "./devices/..."

api/api_test.go

@@ -13,9 +13,10 @@ import (
 	"testing"
 	"time"
 
-	"github.com/hashicorp/nomad/api/internal/testutil"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+
+	"github.com/hashicorp/nomad/api/internal/testutil"
 )
 
 type configCallback func(c *Config)
@@ -538,3 +539,28 @@ func TestCloneHttpClient(t *testing.T) {
 	})
 
 }
+
+func TestClient_HeaderRaceCondition(t *testing.T) {
+	require := require.New(t)
+
+	conf := DefaultConfig()
+	conf.Headers = map[string][]string{
+		"test-header": {"a"},
+	}
+	client, err := NewClient(conf)
+	require.NoError(err)
+
+	c := make(chan int)
+
+	go func() {
+		req, _ := client.newRequest("GET", "/any/path/will/do")
+		r, _ := req.toHTTP()
+		c <- len(r.Header)
+	}()
+	req, _ := client.newRequest("GET", "/any/path/will/do")
+	r, _ := req.toHTTP()
+
+	require.Len(r.Header, 2, "local request should have two headers")
+	require.Equal(2, <-c, "goroutine  request should have two headers")
+	require.Len(conf.Headers, 1, "config headers should not mutate")
+}