diff --git a/.simplecov b/.simplecov
index 5b80c52..5dc758e 100644
--- a/.simplecov
+++ b/.simplecov
@@ -1,5 +1,6 @@
 if ENV['COVERAGE']
   SimpleCov.start do
+    enable_coverage :branch # available in ruby >= 2.5, already required by actionpack 6
     add_filter '/spec/'
   end
 end
diff --git a/AUTHORS.md b/AUTHORS.md
index 21b661d..ae0f9b3 100644
--- a/AUTHORS.md
+++ b/AUTHORS.md
@@ -16,6 +16,7 @@ Redis Session Store authors
 - Olek Poplavsky
 - Tim Lossen
 - Todd Bealmear
+- Vasily Fedoseyev
 - Aleksey Dashkevych
 - Olle Jonsson
 - Nicolas Rodriguez
diff --git a/lib/redis-session-store.rb b/lib/redis-session-store.rb
index d713e7b..a969413 100644
--- a/lib/redis-session-store.rb
+++ b/lib/redis-session-store.rb
@@ -4,6 +4,7 @@
 # the MemCacheStore code, simply dropping in Redis instead.
 class RedisSessionStore < ActionDispatch::Session::AbstractSecureStore
   VERSION = '0.11.5'.freeze
+  # :nocov:
   # Rails 3.1 and beyond defines the constant elsewhere
   unless defined?(ENV_SESSION_OPTIONS_KEY)
     ENV_SESSION_OPTIONS_KEY = if Rack.release.split('.').first.to_i > 1
@@ -12,6 +13,7 @@ class RedisSessionStore < ActionDispatch::Session::AbstractSecureStore
                                 Rack::Session::Abstract::ENV_SESSION_OPTIONS_KEY
                               end
   end
+  # :nocov:
 
   USE_INDIFFERENT_ACCESS = defined?(ActiveSupport).freeze
   # ==== Options
diff --git a/spec/redis_session_store_spec.rb b/spec/redis_session_store_spec.rb
index 16578fb..66854c1 100644
--- a/spec/redis_session_store_spec.rb
+++ b/spec/redis_session_store_spec.rb
@@ -252,21 +252,54 @@
 
       context 'when session id does not exist in redis' do
         it 'returns false' do
-          expect(redis).to receive(:exists).with('foo').and_return(false)
+          expect(redis).to receive(:exists?).with('foo').and_return(false)
           expect(store.send(:session_exists?, :env)).to eq(false)
         end
       end
 
       context 'when session id exists in redis' do
         it 'returns true' do
-          expect(redis).to receive(:exists).with('foo').and_return(true)
+          expect(redis).to receive(:exists?).with('foo').and_return(true)
           expect(store.send(:session_exists?, :env)).to eq(true)
         end
       end
 
       context 'when redis is down' do
-        it 'returns true (fallback to old behavior)' do
+        before do
           allow(store).to receive(:redis).and_raise(Redis::CannotConnectError)
+        end
+
+        it 'returns true (fallback to old behavior)' do
+          expect(store.send(:session_exists?, :env)).to eq(true)
+        end
+
+        context 'when :on_redis_down re-raises' do
+          before { store.on_redis_down = ->(e, *) { raise e } }
+
+          it 'explodes' do
+            expect do
+              store.send(:session_exists?, :env)
+            end.to raise_error(Redis::CannotConnectError)
+          end
+        end
+      end
+
+      context 'when redis does suport exists?' do
+        it 'calls it' do
+          expect(redis).to receive(:exists?).and_return(false)
+          expect(redis).not_to receive(:exists)
+          store.send(:session_exists?, :env)
+        end
+      end
+
+      context 'when redis does not support #exists?' do
+        before do
+          allow(redis).to receive(:respond_to?).with(:exists?).and_return(false)
+          allow(redis).to receive(:exists?).and_raise('shouhld not be called')
+        end
+
+        it 'uses old method exist' do
+          expect(redis).to receive(:exists).with('foo').and_return(true)
           expect(store.send(:session_exists?, :env)).to eq(true)
         end
       end
@@ -345,6 +378,15 @@
         store.send(:destroy, env)
       end
 
+      context 'when no cookie hash in request' do
+        let(:env) { {} }
+
+        it 'does nothing' do
+          allow(store).to receive(:redis).and_return(double('redis'))
+          store.send(:destroy, env)
+        end
+      end
+
       context 'when redis is down' do
         before do
           allow(store).to receive(:redis).and_raise(Redis::CannotConnectError)
@@ -546,9 +588,10 @@ def self.dump(_value)
   end
 
   describe 'setting the session' do
+    let(:env) { { 'rack.session.options' => {} } }
+    let(:sid) { 1234 }
+
     it 'allows changing the session' do
-      env = { 'rack.session.options' => {} }
-      sid = 1234
       allow(store).to receive(:redis).and_return(Redis.new)
       data1 = { 'foo' => 'bar' }
       store.send(:set_session, env, sid, data1)
@@ -560,7 +603,6 @@ def self.dump(_value)
 
     it 'allows changing the session when the session has an expiry' do
       env = { 'rack.session.options' => { expire_after: 60 } }
-      sid = 1234
       allow(store).to receive(:redis).and_return(Redis.new)
       data1 = { 'foo' => 'bar' }
       store.send(:set_session, env, sid, data1)
@@ -569,5 +611,33 @@ def self.dump(_value)
       _, session = store.send(:get_session, env, sid)
       expect(session).to eq(data2)
     end
+
+    context 'when redis is down' do
+      let(:redis_exception_type) { Redis::CannotConnectError }
+
+      before { allow(store).to receive(:redis).and_raise(redis_exception_type) }
+
+      it 'returns false' do
+        expect(store.send(:set_session, env, sid, { 'foo' => 'bar' })).to eq false
+      end
+
+      it 'calls on_redis_down' do
+        store.on_redis_down = double('on_redis_down')
+        expect(store.on_redis_down).to receive(:call).with(
+          be_kind_of(redis_exception_type), env, sid
+        )
+        store.send(:set_session, env, sid, { 'foo' => 'bar' })
+      end
+
+      context 'when :on_redis_down re-raises' do
+        before { store.on_redis_down = ->(e, *) { raise e } }
+
+        it 'explodes' do
+          expect do
+            store.send(:set_session, env, sid, { 'foo' => 'bar' })
+          end.to raise_error(Redis::CannotConnectError)
+        end
+      end
+    end
   end
 end