add docs in README

packages/snaps-jest/README.md

@@ -194,7 +194,7 @@ All properties are optional, and have sensible defaults. The addresses are
 randomly generated by default. Most values can be specified as a hex string, or
 a decimal number.
 
-It returns an object with the user interface that was shown by the snap, in the
+It returns a `getInterface` function that gets the user interface that was shown by the snap, in the
 [onTransaction](https://docs.metamask.io/snaps/reference/exports/#ontransaction)
 function.
 
@@ -214,7 +214,9 @@ describe('MySnap', () => {
       nonce: '0x0',
     });
 
-    expect(response).toRender(panel([text('Hello, world!')]));
+    const screen = response.getInterface();
+
+    expect(screen).toRender(panel([text('Hello, world!')]));
   });
 });
 ```
@@ -233,7 +235,7 @@ All properties are optional, and have sensible defaults. The addresses are
 randomly generated by default. Most values can be specified as a hex string, or
 a decimal number.
 
-It returns an object with the user interface that was shown by the snap, in the
+It returns a `getInterface` function that gets the user interface that was shown by the snap, in the
 [onSignature](https://docs.metamask.io/snaps/reference/exports/#onsignature)
 function.
 
@@ -246,7 +248,9 @@ describe('MySnap', () => {
     const { onSignature } = await installSnap(/* optional snap ID */);
     const response = await onSignature();
 
-    expect(response).toRender(
+    const screen = response.getInterface();
+
+    expect(screen).toRender(
       panel([text('You are using the personal_sign method')]),
     );
   });
@@ -303,7 +307,7 @@ describe('MySnap', () => {
 ### `snap.onHomePage`
 
 The `onHomePage` function can be used to request the home page of the snap. It
-takes no arguments, and returns a promise that resolves to the response from the
+takes no arguments, and returns a promise that contains a `getInterface` function to get the response from the
 [onHomePage](https://docs.metamask.io/snaps/reference/entry-points/#onhomepage)
 function.
 
@@ -318,7 +322,9 @@ describe('MySnap', () => {
       params: [],
     });
 
-    expect(response).toRender(/* ... */);
+    const screen = response.getInterface();
+
+    expect(screen).toRender(/* ... */);
   });
 });
 ```
@@ -344,14 +350,16 @@ assert that a response from a snap matches an expected value:
 
 ### Interacting with user interfaces
 
+#### `snap_dialog`
+
 If your snap uses `snap_dialog` to show user interfaces, you can use the
 `request.getInterface` function to interact with them. This method is present on
 the return value of the `snap.request` function.
 
 It waits for the user interface to be shown, and returns an object with
 functions that can be used to interact with the user interface.
 
-#### Example
+##### Example
 
 ```js
 import { installSnap } from '@metamask/snaps-jest';
@@ -384,6 +392,91 @@ describe('MySnap', () => {
 });
 ```
 
+#### handlers
+
+If your snap uses handlers that shows user interfaces (`onTransaction`, `onSignature`, `onHomePage`), you can use the
+`response.getInterface` function to interact with them. This method is present on
+the return value of the `snap.request` function.
+
+It returns an object with functions that can be used to interact with the user interface.
+
+##### Example
+
+```js
+import { installSnap } from '@metamask/snaps-jest';
+
+describe('MySnap', () => {
+  it('should do something', async () => {
+    const { onHomePage } = await installSnap(/* optional snap ID */);
+    const response = await onHomePage({
+      method: 'foo',
+      params: [],
+    });
+
+    const screen = response.getInterface();
+
+    expect(screen).toRender(/* ... */);
+  });
+});
+```
+
+### User interactions in user interfaces
+
+The object returned by the `getInterface` function exposes other functions to trigger user interactions in the user interface.
+
+- `clickElement(elementName)`: Click on a button inside the user interface. If the button with the given name does not exist in the interface this method will throw.
+- `typeInField(elementName, valueToType)`: Enter a value in a field inside the user interface. If the input field with the given name des not exist in the interface this method will throw.
+
+#### Example
+
+```js
+import { installSnap } from '@metamask/snaps-jest';
+
+describe('MySnap', () => {
+  it('should do something', async () => {
+    const { onHomePage } = await installSnap(/* optional snap ID */);
+    const response = await onHomePage({
+      method: 'foo',
+      params: [],
+    });
+
+    const screen = response.getInterface();
+
+    expect(screen).toRender(/* ... */);
+
+    await screen.clickElement('myButton');
+
+    const screen = response.getInterface();
+
+    expect(screen).toRender(/* ... */);
+  });
+});
+```
+
+```js
+import { installSnap } from '@metamask/snaps-jest';
+
+describe('MySnap', () => {
+  it('should do something', async () => {
+    const { onHomePage } = await installSnap(/* optional snap ID */);
+    const response = await onHomePage({
+      method: 'foo',
+      params: [],
+    });
+
+    const screen = response.getInterface();
+
+    expect(screen).toRender(/* ... */);
+
+    await screen.typeInField('myField', 'the value to type');
+
+    const screen = response.getInterface();
+
+    expect(screen).toRender(/* ... */);
+  });
+});
+```
+
 ## Options
 
 You can pass options to the test environment by adding a