test GOPACKGE env var usage

cmd/muxt/testdata/generate/generate_env_vars.txtar

@@ -0,0 +1,52 @@
+env GOPACKAGE=server
+
+muxt generate
+
+exec go test -cover
+
+-- template.gohtml --
+{{define "GET /" }}<h1>Hello, world!</h1>{{end}}
+
+-- go.mod --
+module server
+
+go 1.22
+
+-- template.go --
+package server
+
+import (
+	"embed"
+	"html/template"
+)
+
+//go:embed *.gohtml
+var formHTML embed.FS
+
+var templates = template.Must(template.ParseFS(formHTML, "*"))
+-- template_test.go --
+package server
+
+import (
+	"testing"
+
+	"net/http"
+	"net/http/httptest"
+)
+
+func Test(t *testing.T) {
+	mux := http.NewServeMux()
+
+	routes(mux, nil)
+
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	rec := httptest.NewRecorder()
+
+	mux.ServeHTTP(rec, req)
+
+	res := rec.Result()
+
+	if res.StatusCode != http.StatusOK {
+		t.Error("expected OK")
+	}
+}