Add unit test on ScanEncryptorUtils.

[bmarty]

Type of change

• Feature
• Bugfix
• Technical
• Other :

Content

Add test to check that content can be decrypted. When we will switch to Vodozemac, the test will be updated, to ensure that content encrypted by libolm will be decryptable by Vodozemac.

Motivation and context

Part of libolm removal.

CC @poljar @Velin92

Screenshots / GIFs

Tests

• Step 1
• Step 2
• Step ...

Tested devices

• Physical
• Emulator
• OS version(s):

Checklist

• Changes has been tested on an Android device or Android emulator with API 21
• UI change has been tested on both light and dark themes
• Accessibility has been taken into account. See https://github.com/element-hq/element-android/blob/develop/CONTRIBUTING.md#accessibility
• Pull request is based on the develop branch
• Pull request includes a new file under ./changelog.d. See https://github.com/element-hq/element-android/blob/develop/CONTRIBUTING.md#changelog
• Pull request includes screenshots or videos if containing UI changes
• Pull request includes a sign off
• You've made a self review of your PR
• If you have modified the screen flow, or added new screens to the application, you have updated the test UiAllScreensSanityTest.allScreensTest()

[BillCarsonFr]

Just a nit

[BillCarsonFr]

and what happens when one is provided :D ?

[bmarty]

Yes, at the beginning, the test was named whenServerKeyIsProvidedTheContentIsEncrypted, but then I renamed it. I will add another test to cover this.