Handle rounding errors for min_score requirements

refs LS-1916
flag=none

Uses BigDecimal when comparing scores for min_score completion
requirements.

test plan: automated :)

The best way to test this locally is to:
- Create a course with a student
- Create a module and add an assignment to that module
- Make the assignment worth 10 points
- Add a module completion requirement for the assignment to
  score at least 1
- Publish the module and the assignment
- In the UI, give the student a grade of 0 for the assignment
- As the student, see that the item is incomplete
- From the rails console, find the submission and give it
  a score of 0.3 + 0.3 + 0.3 + 0.1

```
submission = Submission.last
submission.score = 0.3 + 0.3 + 0.3 + 0.1 # 0.9999999999
submission.save
```

- As the student, refresh the modules page
- See that the module item is marked as complete
- View the module item in the api and verify it is marked as complete
  there too `/api/v1/modules/:module_id`

Change-Id: I428fef5eb73e07ed64b5e43509159b9317d4645d
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/260593
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Eric Saupe <eric.saupe@instructure.com>
QA-Review: Eric Saupe <eric.saupe@instructure.com>
Product-Review: Nate Armstrong <narmstrong@instructure.com>

app/models/context_module_progression.rb

@@ -275,7 +275,7 @@ class ContextModuleProgression < ActiveRecord::Base
 
     subs.any? do |sub|
       score = get_submission_score(sub)
-      requirement_met = (score.present? && score >= requirement[:min_score].to_f)
+      requirement_met = (score.present? && score.to_d >= requirement[:min_score].to_f)
       if requirement_met
         remove_incomplete_requirement(requirement[:id])
       else

spec/apis/v1/context_modules_api_spec.rb

@@ -800,6 +800,27 @@ describe "Modules API", type: :request do
       expect(json['completed_at']).not_to be_nil
     end
 
+    it "should consider scores that are close enough as complete" do
+      teacher = @course.enroll_teacher(User.create!, enrollment_state: 'active').user
+      @module1.completion_requirements = {
+        @assignment_tag.id => { :type => 'min_score', :min_score => 1 },
+      }
+      @module1.save!
+
+      json = api_call(:get, "/api/v1/courses/#{@course.id}/modules/#{@module1.id}",
+                      :controller => "context_modules_api", :action => "show", :format => "json",
+                      :course_id => "#{@course.id}", :id => "#{@module1.id}")
+      expect(json['state']).to eq 'unlocked'
+
+      @assignment.grade_student(@user, score: 0.3 + 0.3 + 0.3 + 0.1, grader: teacher)
+
+      json = api_call(:get, "/api/v1/courses/#{@course.id}/modules/#{@module1.id}",
+                      :controller => "context_modules_api", :action => "show", :format => "json",
+                      :course_id => "#{@course.id}", :id => "#{@module1.id}")
+      expect(json['state']).to eq 'completed'
+      expect(json['completed_at']).not_to be_nil
+    end
+
     context 'show including content details' do
       let(:module1_json) do
         api_call(:get, "/api/v1/courses/#{@course.id}/modules/#{@module1.id}?include[]=items&include[]=content_details",

spec/models/context_module_progression_spec.rb

@@ -170,12 +170,25 @@ describe ContextModuleProgression do
     context "when post policies enabled" do
       let(:assignment) { @course.assignments.create! }
       let(:tag) { @module.add_item({id: assignment.id, type: "assignment"}) }
+      let(:min_score) { 90 }
 
       before(:each) do
-        @module.update!(completion_requirements: {tag.id => {type: "min_score", min_score: 90}})
+        @module.update!(completion_requirements: {tag.id => {type: "min_score", min_score: min_score}})
         @submission = assignment.submit_homework(@user, body: "my homework")
       end
 
+      context 'when the score is close enough' do
+        let(:min_score) { 1 }
+        let(:score) { 0.9999999999999999 } # eg 0.3 + 0.3 + 0.3 + 0.1
+
+        it 'evaluates requirement as complete' do
+          @submission.update!(score: score, posted_at: 1.second.ago)
+          progression = @module.context_module_progressions.find_by(user: @user)
+          requirement = {id: tag.id, type: 'min_score', min_score: min_score}
+          expect(progression.requirements_met).to include requirement
+        end
+      end
+
       it "doesn't mark students that haven't submitted as in-progress" do
         other_student = student_in_course(:course => @course, :active_all => true).user
         progression = @module.evaluate_for(other_student)