add e2e tests to locality -> occurrence, and fix occurrence creation modal save button not disabling properly

cypress/e2e/locality.cy.js

@@ -493,6 +493,38 @@ describe('Editing a locality', () => {
     cy.visit(`/locality/20920?tab=5`)
     cy.contains('wet_screen')
   })
+
+  it('and creating a new Occurrence through the Occurrences tab works', () => {
+    cy.visit(`/locality/20920?tab=3`)
+    cy.get('[id=edit-button]').click()
+    cy.contains('Open occurrence creation view').click()
+    cy.contains('Save occurrence').should('be.disabled')
+
+    cy.contains('Select Species').click()
+    cy.get('[data-cy=table-cell-species_name]').first().click()
+    cy.contains('simplicidens')
+    cy.contains('Close').click()
+    cy.get('[id=nis-textfield]').type('1221')
+    cy.contains('Save occurrence').click()
+
+    cy.addReferenceAndSave()
+    cy.visit(`/locality/20920?tab=3`)
+    cy.contains('simplicidens')
+    cy.contains('1221')
+  })
+
+  it('and creating a new Occurrence does not show species that are already used in other Occurrences', () => {
+    cy.visit(`/locality/21050?tab=3`)
+    cy.contains('meneghinii')
+    cy.get('simplicidens').should('not.exist')
+    cy.get('legidensis').should('not.exist')
+    cy.get('[id=edit-button]').click()
+    cy.contains('Open occurrence creation view').click()
+    cy.contains('Select Species').click()
+    cy.get('meneghinii').should('not.exist')
+    cy.contains('simplicidens')
+    cy.contains('legidensis')
+  })
 })
 
 describe('Locality table filtering', () => {

frontend/src/components/Locality/Tabs/OccurrencesTab.tsx

@@ -115,6 +115,10 @@ const NewOccurrenceDialogContent = ({
     return Object.keys(nextFieldsWithErrors).length === 0
   }
 
+  const speciesSelected = () => {
+    return editData.species_name && editData.species_name.length > 0
+  }
+
   const handleSave = () => {
     if (!validateAllFields()) {
       notify('Please fix occurrence validation errors before saving.', 'error')
@@ -162,7 +166,7 @@ const NewOccurrenceDialogContent = ({
       <DialogActions>
         <Button onClick={onClose}>Cancel</Button>
         <Button
-          disabled={Object.keys(fieldsWithErrors).length > 0}
+          disabled={!speciesSelected() || Object.keys(fieldsWithErrors).length > 0}
           onClick={() => void handleSave()}
           startIcon={<SaveIcon />}
           variant="contained"