Kolibri: The same resource can be added twice to a lesson

[metodimilevqa]

Observed behavior

Scenario: Preview a resource from the search results and add/remove it to and from the lesson

• I am on the preview page for exercise and I click ADD button, I'm returned to the previous screen with the search results. There I see the checkbox selected for the added resource but I can again go to the preview page for the exercise I already added and I can add it one more time. So I have the same resource added twice to the lesson. Then when I go back to the Lesson screen and click Remove for one of them, both are deleted.
  

Expected behavior

The user can't add a resource to the lesson if this resource is already added beforehand. Possible solution: Disable the ADD button of already added resources in the preview resource page.

User-facing consequences

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Errors and logs

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Steps to reproduce

Preconditions:
I am signed in to Kolibri as a coach user
I am on the Coach > Class > Plan > Lessons page
There is a channel and topic on the device
There is a Lesson already created

1. Click a Lesson
2. Click Manage Resources button
3. Browse down to a single topic
4. Click ADD
5. After returned to the topics list click again the card of the topic you just added
6. Click ADD - the topic is again added

Context

Kolibri 0.14.3
Raspberry Pi 4
OS: Raspbian GNU, Linux 10
Chrome (Latest) + Firefox (Latest)

[pcenov]

Retested today on Kolibri v0.14.7-rc2 and this is no longer an issue because as soon as one clicks the Add button the page gets reloaded, the button changes to Remove and there's a text to the left of it stating that the resource has been 'Added':