Add some tests for modified Static.

handler/misc.go

@@ -64,6 +64,10 @@ func Ready(ms storage.MetricStore) http.Handler {
 //
 // The returned handler is already instrumented for Prometheus.
 func Static(root http.FileSystem, prefix string) http.Handler {
+	if prefix == "/" {
+		prefix = ""
+	}
+
 	handler := http.FileServer(root)
 	return promhttp.InstrumentHandlerCounter(
 		httpCnt.MustCurryWith(prometheus.Labels{"handler": "static"}),

handler/misc_test.go

@@ -0,0 +1,62 @@
+package handler
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"testing"
+)
+
+type fakeFileSystem struct {
+	files map[string]struct{}
+}
+
+// Open implements the http.FileSystem interface
+//
+// If a file is present, no error will be returned.
+// This implementation always returns a nil File.
+func (f *fakeFileSystem) Open(name string) (http.File, error) {
+	log.Println("requesting" + name)
+
+	if _, ok := f.files[name]; !ok {
+		return nil, os.ErrNotExist
+	}
+	return os.Open("misc_test.go")
+	//	return nil, nil
+}
+
+func TestRoutePrefixForStatic(t *testing.T) {
+	fs := &fakeFileSystem{map[string]struct{}{
+		"/index.js": struct{}{},
+	}}
+
+	for _, test := range []struct {
+		prefix string
+		path   string
+		code   int
+	}{
+		{"/", "/index.js", 200},
+		{"/", "/missing.js", 404},
+		{"/route-prefix", "/index.js", 200},
+		{"/route-prefix", "/missing.js", 404},
+	} {
+		test := test
+		t.Run(fmt.Sprintf("%v", test), func(t *testing.T) {
+			t.Parallel()
+			req, err := http.NewRequest(
+				http.MethodGet, "http://example.com"+test.prefix+test.path, nil,
+			)
+			if err != nil {
+				t.Fatal(err)
+			}
+			w := httptest.NewRecorder()
+			static := Static(fs, test.prefix)
+			static.ServeHTTP(w, req)
+			if test.code != w.Code {
+				t.Errorf("Wanted %d, got %d.", test.code, w.Code)
+			}
+		})
+	}
+}