Fix end-to-end tests for end-to-end encryption verification

Fixes https://github.com/vector-im/riot-web/issues/13226

This isn't the fastest route, but it is a predictable route for the happy path we probably want to test. For example, Alice will already be staring at the DM and could easily accept the verification there, but we probably want to make sure that the toast is present and does the right thing. Similarly, neither of them need to verify that there's green shields everywhere, they should be implied, however an explicit check follows a real user's gaze.

src/components/views/right_panel/VerificationPanel.js

@@ -123,10 +123,17 @@ export default class VerificationPanel extends React.PureComponent {
             const sasLabel = showQR ?
                 _t("If you can't scan the code above, verify by comparing unique emoji.") :
                 _t("Verify by comparing unique emoji.");
+
+            // Note: mx_VerificationPanel_verifyByEmojiButton is for the end-to-end tests
             sasBlock = <div className="mx_UserInfo_container">
                 <h3>{_t("Verify by emoji")}</h3>
                 <p>{sasLabel}</p>
-                <AccessibleButton disabled={disabled} kind="primary" className="mx_UserInfo_wideButton" onClick={this._startSAS}>
+                <AccessibleButton
+                    disabled={disabled}
+                    kind="primary"
+                    className="mx_UserInfo_wideButton mx_VerificationPanel_verifyByEmojiButton"
+                    onClick={this._startSAS}
+                >
                     {_t("Verify by emoji")}
                 </AccessibleButton>
             </div>;