diff --git a/spec/controllers/ajax/subscription_controller_spec.rb b/spec/controllers/ajax/subscription_controller_spec.rb
new file mode 100644
index 00000000..6c82f400
--- /dev/null
+++ b/spec/controllers/ajax/subscription_controller_spec.rb
@@ -0,0 +1,160 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+describe Ajax::SubscriptionController, :ajax_controller, type: :controller do
+  # need to use a different user here, as after a create the user owning the
+  # answer is automatically subscribed to it
+  let(:answer_user) { FactoryBot.create(:user) }
+  let(:answer) { FactoryBot.create(:answer, user: answer_user) }
+
+  describe "#subscribe" do
+    let(:params) do
+      {
+        answer: answer_id
+      }
+    end
+
+    subject { post(:subscribe, params: params) }
+
+    context "when user is signed in" do
+      before(:each) { sign_in(user) }
+
+      context "when answer exists" do
+        let(:answer_id) { answer.id }
+        let(:expected_response) do
+          {
+            "success" => true,
+            "status" => 418,
+            "message" => anything
+          }
+        end
+
+        context "when subscription does not exist" do
+          it "creates a subscription on the answer" do
+            expect { subject }.to(change { answer.subscriptions.count }.by(1))
+            expect(answer.subscriptions.where(is_active: true).map { |s| s.user.id }.sort).to eq([answer_user.id, user.id].sort)
+          end
+
+          include_examples "returns the expected response"
+        end
+
+        context "when subscription already exists" do
+          before(:each) { Subscription.subscribe(user, answer) }
+
+          it "does not modify the answer's subscriptions" do
+            expect { subject }.to(change { answer.subscriptions.count }.by(0))
+            expect(answer.subscriptions.where(is_active: true).map { |s| s.user.id }.sort).to eq([answer_user.id, user.id].sort)
+          end
+
+          include_examples "returns the expected response"
+        end
+      end
+
+      context "when answer does not exist" do
+        let(:answer_id) { "Bielefeld" }
+        let(:expected_response) do
+          {
+            "success" => false,
+            "status" => "not_found",
+            "message" => anything
+          }
+        end
+
+        it "does not create a new subscription" do
+          expect { subject }.not_to(change { Subscription.count })
+        end
+
+        include_examples "returns the expected response"
+      end
+    end
+
+    context "when user is not signed in" do
+      let(:answer_id) { answer.id }
+
+      it "redirects to somewhere else, apparently" do
+        subject
+        expect(response).to be_a_redirect
+      end
+    end
+  end
+
+  describe "#unsubscribe" do
+    let(:params) do
+      {
+        answer: answer_id
+      }
+    end
+
+    subject { post(:unsubscribe, params: params) }
+
+    context "when user is signed in" do
+      before(:each) { sign_in(user) }
+
+      context "when answer exists" do
+        let(:answer_id) { answer.id }
+        let(:expected_response) do
+          {
+            "success" => true,
+            "status" => 418,
+            "message" => anything
+          }
+        end
+
+        context "when subscription exists" do
+          before(:each) { Subscription.subscribe(user, answer) }
+
+          it "removes an active subscription from the answer" do
+            expect { subject }.to(change { answer.subscriptions.where(is_active: true).count }.by(-1))
+            expect(answer.subscriptions.where(is_active: true).map { |s| s.user.id }.sort).to eq([answer_user.id].sort)
+          end
+
+          include_examples "returns the expected response"
+        end
+
+        context "when subscription does not exist" do
+          let(:expected_response) do
+            {
+              "success" => false,
+              "status" => 418,
+              "message" => anything
+            }
+          end
+
+          it "does not modify the answer's subscriptions" do
+            expect { subject }.to(change { answer.subscriptions.count }.by(0))
+            expect(answer.subscriptions.where(is_active: true).map { |s| s.user.id }.sort).to eq([answer_user.id].sort)
+          end
+
+          include_examples "returns the expected response"
+        end
+      end
+
+      context "when answer does not exist" do
+        let(:answer_id) { "Bielefeld" }
+        let(:expected_response) do
+          {
+            "success" => false,
+            "status" => "not_found",
+            "message" => anything
+          }
+        end
+
+        it "does not create a new subscription" do
+          expect { subject }.not_to(change { Subscription.count })
+        end
+
+        include_examples "returns the expected response"
+      end
+    end
+
+    context "when user is not signed in" do
+      let(:answer_id) { answer.id }
+
+      it "redirects to somewhere else, apparently" do
+        subject
+        expect(response).to be_a_redirect
+      end
+    end
+  end
+end