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\#S:MODE=test
\#S:EXTERNAL=rust=hello_test.rs
\#S:EXTERNAL=javascript=hello_test.js=test
# Hello Test Tutorial
Welcome to the Hello Test tutorial. Today you will be learning how to test your Holochain apps. This tutorial will add to the previous [Hello Holo]() tutorial, so make sure you do that one first.
Testing is a really important part of building higher quality apps but it's also a an excellent way to think through how your app will be used.
## Understand the tests
When you ran `hc init` in the previous tutorial Holochain already generated some tests for you.
The tests are written in JavaScript and use the Holochain testing framework [Diorama](https://github.com/holochain/diorama), along with a popular test harness called [Tape](https://github.com/substack/tape). You can run them with [Node.JS](https://nodejs.org/en/), a runtime that lets you execute JavaScript in the terminal.
Open up the `cc_tuts/test/index.js` in your favourite text editor. Have a look through the code.
Imports required to do testing:
\#S:INCLUDE
```javascript
const path = require('path')
const tape = require('tape')
const { Diorama, tapeExecutor, backwardCompatibilityMiddleware } = require('@holochain/diorama')
```
This is a catch-all error logger that will let you know if a `Promise` fails and there's no error handler to hear it. [`Promise`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)s are a way of simplifying complex asynchronous code, and Diorama uses a lot of them.
```javascript
process.on('unhandledRejection', error => {
console.error('got unhandledRejection:', error);
});
```
The path to your compiled DNA.
```javascript
const dnaPath = path.join(__dirname, "../dist/cc_tuts.dna.json")
const dna = Diorama.dna(dnaPath, 'cc_tuts')
```
Setup a testing scenario.
This creates two agents: Alice and Bob.
```javascript
const diorama = new Diorama({
instances: {
alice: dna,
bob: dna,
},
bridges: [],
debugLog: false,
executor: tapeExecutor(require('tape')),
middleware: backwardCompatibilityMiddleware,
})
```
This is the test that Holochain generated based on the `my_entry` struct and the zome functions that work with it. We removed them in our Hello Holo tutorial, so let's remove the test.
Remove the following section:
\#S:SKIP
```javascript
diorama.registerScenario("description of example test", async (s, t, { alice }) => {
// Make a call to a Zome function
// indicating the function, and passing it an input
const addr = await alice.call("my_zome", "create_my_entry", {"entry" : {"content":"sample content"}})
const result = await alice.call("my_zome", "get_my_entry", {"address": addr.Ok})
// check for equality of the actual and expected results
t.deepEqual(result, { Ok: { App: [ 'my_entry', '{"content":"sample content"}' ] } })
})
```
This line will run the tests that you have set up.
```javascript
diorama.run()
```
## Create a test scenario
Tests are organized by creating scenarios. Think of them as a series of actions that the user or group of users take when interacting with your app.
For this test you simply want to get the Alice user to call the `hello_holo` zome function. Then check that you get the result `Hello Holo`.
Place the following just above `diorama.run()`.
Register a test scenario that checks `hello_holo()` returns the correct value:
\#S:INCLUDE
```javascript
diorama.registerScenario("Test hello holo", async (s, t, { alice }) => {
```
Make a call to the `hello_holo` Zome function, passing no arguments:
```javascript
const result = await alice.call("hello", "hello_holo", {});
```
Make sure the result is okay:
```javascript
t.ok(result.Ok);
```
Check that the result matches what you expected:
```javascript
t.deepEqual(result, { Ok: 'Hello Holo' })
})
```
\#S:INCLUDE,HIDE
```javascript
diorama.run()
```
## Run the test
\#S:CHECK=javascript
Now in the `hello_helo` directory, run the test like this:
```bash
$ hc test
```
This will compile and run the test scenario you just wrote. You will see a lot of output.
!!! success "If everything went okay, then right at the end you will see:"
```
# tests 2
# pass 2
# ok
```
Congratulations; you have tested your first Holochain app. Look at you go! :sparkles:
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