Skip to main content

How to test Gno Code


In this guide, we will explore the available tooling in testing out the Gno Realms and Packages we write. We will go over different CLI tools available to developers, gno testing libraries as well as testing techniques that involve data mocking.


Example Realm

For the purpose of this guide, we will be testing the simple Counter Realm created in the How to write a simple Gno Smart Contract (Realm) guide.

// counter-app/r/counter/counter.gno

package counter

import (

var count int

func Increment() {

func Decrement() {

func Render(_ string) string {
return ufmt.Sprintf("Count: %d", count)

1. Writing the Gno test

Gno tests are written in the same manner and format as regular Go tests, just in _test.gno files.

We can place the Gno tests for the Counter Realm in the same directory as counter.gno:

├─ r/
│ ├─ counter/
│ │ ├─ counter.gno
│ │ ├─ counter_test.gno <--- the test source code
cd counter
touch counter_test.gno

What should be tested in this Counter Realm example? Mainly, we want to verify that:

  • Increment increments the value.
  • Decrement decrements the value.
  • Render returns a valid formatted value.

Let's write the required unit tests:

// counter-app/r/counter/counter_test.gno

package counter

import "testing"

func TestCounter_Increment(t *testing.T) {
// Reset the value
count = 0

// Verify the initial value is 0
if count != 0 {
t.Fatalf("initial value != 0")

// Increment the value

// Verify the initial value is 1
if count != 1 {
t.Fatalf("initial value != 1")

func TestCounter_Decrement(t *testing.T) {
// Reset the value
count = 0

// Verify the initial value is 0
if count != 0 {
t.Fatalf("initial value != 0")

// Decrement the value

// Verify the initial value is 1
if count != -1 {
t.Fatalf("initial value != -1")

func TestCounter_Render(t *testing.T) {
// Reset the value
count = 0

// Verify the Render output
if Render("") != "Count: 0" {
t.Fatalf("invalid Render value")
Testing package-level variables

In practice, it is not advisable to test and validate package level variables like this, as their value is mutated between test runs. For the sake of keeping this guide simple, we went ahead and reset the variable value for each test, however, you should employ more robust test strategies.

2. Running the Gno test

To run the prepared Gno tests, we can utilize the gno test CLI tool.

Simply point it to the location containing our testing source code, and the tests will execute. For example, we can run the following command from the counter-app/r/counter directory:

gno test -v .

Let's look into the different parts of this command:

  • -v enables the verbose output.
  • -root-dir specifies the root directory to our cloned gno GitHub repository
  • . specifies the location containing our test files. Since we are already located in that directory, we specify a ..

Running the test command should produce a successful output:

=== RUN   TestCounter_Increment
--- PASS: TestCounter_Increment (0.00s)
=== RUN TestCounter_Decrement
--- PASS: TestCounter_Decrement (0.00s)
=== RUN TestCounter_Render
--- PASS: TestCounter_Render (0.00s)
ok ./. 1.00s

Additional test support

As we grow more familiar with Gno development, our Realm / Package logic can become more complex. As such, we need more robust testing support in the form of mocking values ahead of time that would normally be only available on a live (deployed) Realm / Package.

Luckily, the Gno standard library provides ample support for functionality such as setting predefined values ahead of time, such as the request caller address, or the calling package address.

You can learn more about these methods, that are importable using the std import declaration, in the Standard Library reference section.


That's it 🎉

You have successfully written and tested Gno code. Additionally, you have utilized the gno test tool, and understood how it can be configured to make the developer experience smooth.