Validate at least one provider school exists before deleting one

app/services/provider_schools/removal.rb

@@ -28,6 +28,8 @@ def site
     end
 
     def removable?
+      return false if provider.schools.one?
+
       !school.course_schools.joins(:course).merge(Course.kept).exists?
     end
 

spec/services/provider_schools/removal_spec.rb

@@ -3,25 +3,31 @@
 require "rails_helper"
 
 RSpec.describe ProviderSchools::Removal do
-  let(:gias_school) { create(:gias_school, urn: "123456") }
-  let(:site_uuid) { Faker::Internet.uuid }
+  subject(:removal) { described_class.new(provider:, uuid: provider_school.uuid) }
 
-  describe "#call" do
-    let(:provider) { create(:provider) }
-    let!(:site) { create(:site, provider:, urn: gias_school.urn, code: "A", uuid: site_uuid) }
-    let!(:provider_school) { create(:provider_school, provider:, gias_school:, site_code: site.code, uuid: site_uuid) }
+  let(:provider) { create(:provider) }
+
+  # The pair written together when a school is added: the provider school and
+  # the legacy site it shares a uuid, site code and urn with.
+  let!(:site) { create(:site, provider:) }
+  let!(:provider_school) { create(:provider_school, :for_site, site:) }
+
+  # A second school, so removal is never blocked by the last-school guard. It
+  # needs no legacy site of its own: the guard only counts provider schools.
+  let!(:other_provider_school) { create(:provider_school, provider:) }
 
+  describe "#call" do
     it "removes both the legacy site and provider school" do
-      expect(described_class.new(provider:, uuid: site_uuid).call).to be(true)
+      expect(removal.call).to be(true)
 
       expect(Site.where(id: site.id)).to be_empty
       expect(Provider::School.where(id: provider_school.id)).to be_empty
     end
 
     it "does not remove either record when the provider school is attached to a course school" do
-      create(:course_school, course: create(:course, provider:), provider_school:, gias_school:)
+      create(:course_school, course: create(:course, provider:), provider_school:, gias_school: provider_school.gias_school)
 
-      expect(described_class.new(provider:, uuid: site_uuid).call).to be(false)
+      expect(removal.call).to be(false)
 
       expect(Site.where(id: site.id)).to contain_exactly(site)
       expect(Provider::School.where(id: provider_school.id)).to contain_exactly(provider_school)
@@ -30,29 +36,34 @@
     it "does not remove a legacy site that has no provider school" do
       provider_school.destroy!
 
-      expect {
-        described_class.new(provider:, uuid: site_uuid).call
-      }.to raise_error(ActiveRecord::RecordNotFound)
+      expect { described_class.new(provider:, uuid: site.uuid).call }.to raise_error(ActiveRecord::RecordNotFound)
 
       expect(Site.where(id: site.id)).to contain_exactly(site)
     end
 
     it "removes a provider school without requiring a legacy site" do
-      provider_school_without_site = create(:provider_school, provider:)
-
-      expect(described_class.new(provider:, uuid: provider_school_without_site.uuid).call).to be(true)
+      expect(described_class.new(provider:, uuid: other_provider_school.uuid).call).to be(true)
 
-      expect(Provider::School.where(id: provider_school_without_site.id)).to be_empty
+      expect(Provider::School.where(id: other_provider_school.id)).to be_empty
     end
 
     it "does not remove a provider school belonging to another provider" do
-      other_provider_school = create(:provider_school, uuid: Faker::Internet.uuid)
+      someone_elses_school = create(:provider_school)
 
-      expect {
-        described_class.new(provider:, uuid: other_provider_school.uuid).call
-      }.to raise_error(ActiveRecord::RecordNotFound)
+      expect { described_class.new(provider:, uuid: someone_elses_school.uuid).call }.to raise_error(ActiveRecord::RecordNotFound)
 
-      expect(Provider::School.where(id: other_provider_school.id)).to contain_exactly(other_provider_school)
+      expect(Provider::School.where(id: someone_elses_school.id)).to contain_exactly(someone_elses_school)
+    end
+
+    context "when it is the provider's only school" do
+      let!(:other_provider_school) { nil }
+
+      it "does not remove either record" do
+        expect(removal.call).to be(false)
+
+        expect(Site.where(id: site.id)).to contain_exactly(site)
+        expect(Provider::School.where(id: provider_school.id)).to contain_exactly(provider_school)
+      end
     end
 
     # Removal deliberately does not branch on the recruitment cycle: the same
@@ -61,7 +72,7 @@
       let(:provider) { create(:provider, :next_recruitment_cycle) }
 
       it "removes both the legacy site and provider school" do
-        expect(described_class.new(provider:, uuid: site_uuid).call).to be(true)
+        expect(removal.call).to be(true)
 
         expect(Site.where(id: site.id)).to be_empty
         expect(Provider::School.where(id: provider_school.id)).to be_empty