diff --git a/util/util_test.go b/util/util_test.go
new file mode 100644
index 000000000..770d1dd95
--- /dev/null
+++ b/util/util_test.go
@@ -0,0 +1,43 @@
+package util
+
+import (
+	"fmt"
+	"reflect"
+	"testing"
+
+	"github.com/hashicorp/go-cty/cty"
+	"github.com/hashicorp/terraform-plugin-sdk/v2/diag"
+)
+
+func TestValidateTZValueDiagFunc(t *testing.T) {
+	notValidTZ1 := "not a valid TZ"
+
+	cases := []struct {
+		given string
+		want  diag.Diagnostics
+		path  cty.Path
+	}{
+		{
+			given: "America/Montevideo",
+			want:  nil,
+			path:  cty.Path{},
+		},
+		{
+			given: "America/Indiana/Indianapolis",
+			want:  nil,
+			path:  cty.Path{},
+		},
+		{
+			given: notValidTZ1,
+			want:  diag.Diagnostics{diag.Diagnostic{Severity: 0, Summary: fmt.Sprintf("\"%s\" is a not valid input. Please refer to the list of allowed Time Zone values at https://developer.pagerduty.com/docs/1afe25e9c94cb-types#time-zone", notValidTZ1), Detail: "", AttributePath: cty.Path{cty.GetAttrStep{Name: "time_zone"}}}},
+			path:  cty.Path{cty.GetAttrStep{Name: "time_zone"}},
+		},
+	}
+
+	for _, c := range cases {
+		got := ValidateTZValueDiagFunc(c.given, c.path)
+		if !reflect.DeepEqual(got, c.want) {
+			t.Errorf("want %v; got %v", c.want, got)
+		}
+	}
+}