[Class statistics] Fix a bug where change in filtered students didn't…

… trigger a new request for course stats

Also added two tests for this scenario

cypress/e2e/Population_statistics.js

@@ -96,6 +96,46 @@ describe('Population Statistics tests', () => {
       cy.get('[data-cy=toggle-group-module-MAT-tyo]').should('not.exist')
     })
 
+    it('New fetch of courses data is done when curriculum is changed', () => {
+      cy.visit(pathToMathBSc2020)
+      cy.contains('Courses of class').click()
+      cy.intercept('/api/v2/populationstatistics/courses').as('courseData')
+      cy.get('[data-cy=curriculum-picker]').click().contains('2020 - 2023').click()
+      cy.wait('@courseData').then(({ response }) => {
+        expect(response.body).to.have.property('allStudents')
+        expect(response.body).to.have.property('coursestatistics')
+        expect(response.body.allStudents).to.equal(27)
+        expect(response.body.coursestatistics.some(stat => stat.course.code === 'DIGI-100')).to.be.true
+      })
+      cy.get('[data-cy=curriculum-picker]').click().contains('2023 - 2026').click()
+      cy.wait('@courseData').then(({ response }) => {
+        expect(response.body).to.have.property('allStudents')
+        expect(response.body).to.have.property('coursestatistics')
+        expect(response.body.allStudents).to.equal(27)
+        expect(response.body.coursestatistics.some(stat => stat.course.code === 'DIGI-100')).to.be.not.true
+      })
+    })
+
+    it('New fetch of courses data is done when filtered students change', () => {
+      cy.visit(pathToMathBSc2020)
+      cy.contains('Courses of class').click()
+      cy.intercept('/api/v2/populationstatistics/courses').as('courseData')
+      cy.wait('@courseData').then(({ response }) => {
+        expect(response.body).to.have.property('allStudents')
+        expect(response.body).to.have.property('coursestatistics')
+        expect(response.body.allStudents).to.equal(27)
+      })
+      cy.get('[data-cy=GraduatedFromProgramme-filter-card]').within(() => {
+        cy.get('[data-cy=GraduatedFromProgramme-header]').click()
+        cy.get('[data-cy=option-graduated-true]').click()
+        cy.wait('@courseData').then(({ response }) => {
+          expect(response.body).to.have.property('allStudents')
+          expect(response.body).to.have.property('coursestatistics')
+          expect(response.body.allStudents).to.equal(16)
+        })
+      })
+    })
+
     it("Empty 'tags' tab has a link to the page where tags can be created", { retries: 2 }, () => {
       cy.visit(pathToMathBSc2020)
       cy.contains('Students (27)')

services/frontend/src/components/PopulationDetails/PopulationCourses/index.jsx

@@ -53,13 +53,21 @@ export const PopulationCourses = ({
   }, [mandatoryCourses])
 
   useEffect(() => {
+    if (programmeCodesToFetch == null || populationSelectedStudentCourses?.query == null) {
+      return
+    }
+    const { courses, selectedStudents } = populationSelectedStudentCourses.query
     if (
-      programmeCodesToFetch != null &&
-      !isEqual(programmeCodesToFetch, populationSelectedStudentCourses.query.courses)
+      !isEqual(programmeCodesToFetch, courses) ||
+      selectedStudents.length !== filteredStudents.length ||
+      !isEqual(
+        selectedStudents,
+        filteredStudents.map(({ studentNumber }) => studentNumber)
+      )
     ) {
       fetch(programmeCodesToFetch)
     }
-  }, [programmeCodesToFetch])
+  }, [programmeCodesToFetch, filteredStudents])
 
   const pending = populationSelectedStudentCourses.pending || !mandatoryCourses