prefer assignment title over resource link title

why: we used to pass the assignment title as the resource link claims
     title, and customers are expecting this behavior, but we changed
     this at some point to prefer the the resource link title.

fixes: INTEROP-8629
flag=none

test plan:
note:
  it would be easiest if this was QA'd after 8700 has been merged
  (including the commit to the LTI 1.3 Test Tool - or cherry-pick from
  https://gerrit.instructure.com/c/lti-1.3-test-tool/+/351606) and using
  the LTI 1.3 Test Tool you added
  {"https://canvas.instructure.com/lti/preserveExistingAssignmentName": true}
  to the new 'Extra arbitrary content item data' field in the tool
  configuration to ensure that the assignment title is different and not
  overwritten by the tool title or the lineItem.label

- create an assignment with a 1.3 tool that has a title different from
  the assignment title and save
- if using the LTI 1.3 Test Tool you should see in the decoded jwt on
  the assignment view that the resource link claims title is the
  assignment title.

Change-Id: Iac0a74a5c47fdddbaa9a5ab1071c0b846984f0c4
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/351965
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Tucker Mcknight <tmcknight@instructure.com>
QA-Review: Tucker Mcknight <tmcknight@instructure.com>
Product-Review: Alexis Nast <alexis.nast@instructure.com>

lib/lti/messages/resource_link_request.rb

@@ -61,7 +61,7 @@ module Lti::Messages
     def add_resource_link_request_claims!
       @message.resource_link.id = launch_resource_link_id
       @message.resource_link.description = @assignment&.description
-      @message.resource_link.title = resource_link&.title.presence || @assignment&.title.presence || tag_from_resource_link&.title.presence || @context.name
+      @message.resource_link.title = @assignment&.title.presence || resource_link&.title.presence || tag_from_resource_link&.title.presence || @context.name
     end
 
     def add_lti1p1_claims!

spec/lib/lti/messages/resource_link_request_spec.rb

@@ -398,15 +398,44 @@ describe Lti::Messages::ResourceLinkRequest do
 
     it_behaves_like "assignment resource link id check"
 
-    context "the resource link has a blank title but the assignment has a title" do
-      before do
-        expected_assignment_line_item.resource_link.update!(title: "")
-        assignment.update!(title: "foo")
+    context "uses the appropriate title for the resource link claim title" do
+      let(:content_tag) do
+        ContentTag.create!(
+          context: course,
+          title: "fake title",
+          url: "https://example.com",
+          associated_asset: expected_assignment_line_item.resource_link
+        )
       end
 
-      it "uses the assignment title for the resource link title" do
+      before do
+        content_tag
+        assignment.update!(title: "foo")
+        expected_assignment_line_item.resource_link.update!(title: "bar")
+        expected_assignment_line_item.resource_link.content_tag.update!(title: "baz")
+      end
+
+      it "prefers the assignment title over other options" do
         expect(jws[:post_payload].dig("https://purl.imsglobal.org/spec/lti/claim/resource_link", "title")).to eq assignment.title
       end
+
+      it "uses the resource link title if assignment title is blank" do
+        assignment.title = ""
+        expect(jws[:post_payload].dig("https://purl.imsglobal.org/spec/lti/claim/resource_link", "title")).to eq expected_assignment_line_item.resource_link.title
+      end
+
+      it "uses the resource link tag for the title if the assignment title and the resource link title are blank" do
+        assignment.title = ""
+        expected_assignment_line_item.resource_link.update!(title: "")
+        expect(jws[:post_payload].dig("https://purl.imsglobal.org/spec/lti/claim/resource_link", "title")).to eq expected_assignment_line_item.resource_link.content_tag.title
+      end
+
+      it "uses the context name if all other options are blank" do
+        assignment.title = ""
+        expected_assignment_line_item.resource_link.update!(title: "")
+        expected_assignment_line_item.resource_link.content_tag.update!(title: "")
+        expect(jws[:post_payload].dig("https://purl.imsglobal.org/spec/lti/claim/resource_link", "title")).to eq course.name
+      end
     end
   end