diff --git a/activesupport/test/cache/behaviors/local_cache_behavior.rb b/activesupport/test/cache/behaviors/local_cache_behavior.rb
index be610fcb14..968fde93c7 100644
--- a/activesupport/test/cache/behaviors/local_cache_behavior.rb
+++ b/activesupport/test/cache/behaviors/local_cache_behavior.rb
@@ -2,15 +2,16 @@
 
 module LocalCacheBehavior
   def test_instrumentation_with_local_cache
+    key = SecureRandom.uuid
     events = with_instrumentation "write" do
-      @cache.write("foo", "bar")
+      @cache.write(key, SecureRandom.uuid)
     end
     assert_equal @cache.class.name, events[0].payload[:store]
 
     @cache.with_local_cache do
       events = with_instrumentation "read" do
-        @cache.read("foo")
-        @cache.read("foo")
+        @cache.read(key)
+        @cache.read(key)
       end
 
       expected = [@cache.class.name, @cache.send(:local_cache).class.name]
@@ -19,21 +20,24 @@ module LocalCacheBehavior
   end
 
   def test_local_writes_are_persistent_on_the_remote_cache
+    key = SecureRandom.uuid
+    value = SecureRandom.alphanumeric
     retval = @cache.with_local_cache do
-      @cache.write("foo", "bar")
+      @cache.write(key, value)
     end
     assert retval
-    assert_equal "bar", @cache.read("foo")
+    assert_equal value, @cache.read(key)
   end
 
   def test_clear_also_clears_local_cache
+    key = SecureRandom.uuid
     @cache.with_local_cache do
-      @cache.write("foo", "bar")
+      @cache.write(key, SecureRandom.alphanumeric)
       @cache.clear
-      assert_nil @cache.read("foo")
+      assert_nil @cache.read(key)
     end
 
-    assert_nil @cache.read("foo")
+    assert_nil @cache.read(key)
   end
 
   def test_cleanup_clears_local_cache_but_not_remote_cache
@@ -43,79 +47,98 @@ module LocalCacheBehavior
       skip
     end
 
-    @cache.with_local_cache do
-      @cache.write("foo", "bar")
-      assert_equal "bar", @cache.read("foo")
+    key = SecureRandom.uuid
+    value = SecureRandom.alphanumeric
+    other_value = SecureRandom.alphanumeric
 
-      @cache.send(:bypass_local_cache) { @cache.write("foo", "baz") }
-      assert_equal "bar", @cache.read("foo")
+    @cache.with_local_cache do
+      @cache.write(key, value)
+      assert_equal value, @cache.read(key)
+
+      @cache.send(:bypass_local_cache) { @cache.write(key, other_value) }
+      assert_equal value, @cache.read(key)
 
       @cache.cleanup
-      assert_equal "baz", @cache.read("foo")
+      assert_equal other_value, @cache.read(key)
     end
   end
 
   def test_local_cache_of_write
+    key = SecureRandom.uuid
+    value = SecureRandom.alphanumeric
     @cache.with_local_cache do
-      @cache.write("foo", "bar")
-      @peek.delete("foo")
-      assert_equal "bar", @cache.read("foo")
+      @cache.write(key, value)
+      @peek.delete(key)
+      assert_equal value, @cache.read(key)
     end
   end
 
   def test_local_cache_of_read_returns_a_copy_of_the_entry
+    key = SecureRandom.alphanumeric.to_sym
+    value = SecureRandom.alphanumeric
     @cache.with_local_cache do
-      @cache.write(:foo, type: "bar")
-      value = @cache.read(:foo)
-      assert_equal("bar", value.delete(:type))
-      assert_equal({ type: "bar" }, @cache.read(:foo))
+      @cache.write(key, type: value)
+      local_value = @cache.read(key)
+      assert_equal(value, local_value.delete(:type))
+      assert_equal({ type: value }, @cache.read(key))
     end
   end
 
   def test_local_cache_of_read
-    @cache.write("foo", "bar")
+    key = SecureRandom.uuid
+    value = SecureRandom.alphanumeric
+    @cache.write(key, value)
     @cache.with_local_cache do
-      assert_equal "bar", @cache.read("foo")
+      assert_equal value, @cache.read(key)
     end
   end
 
   def test_local_cache_of_read_nil
+    key = SecureRandom.uuid
+    value = SecureRandom.alphanumeric
     @cache.with_local_cache do
-      assert_nil @cache.read("foo")
-      @cache.send(:bypass_local_cache) { @cache.write "foo", "bar" }
-      assert_nil @cache.read("foo")
+      assert_nil @cache.read(key)
+      @cache.send(:bypass_local_cache) { @cache.write(key, value) }
+      assert_nil @cache.read(key)
     end
   end
 
   def test_local_cache_fetch
+    key = SecureRandom.uuid
+    value = SecureRandom.alphanumeric
     @cache.with_local_cache do
-      @cache.send(:local_cache).write_entry "foo", "bar"
-      assert_equal "bar", @cache.send(:local_cache).fetch_entry("foo")
+      @cache.send(:local_cache).write_entry(key, value)
+      assert_equal value, @cache.send(:local_cache).fetch_entry(key)
     end
   end
 
   def test_local_cache_of_write_nil
+    key = SecureRandom.uuid
+    value = SecureRandom.alphanumeric
     @cache.with_local_cache do
-      assert @cache.write("foo", nil)
-      assert_nil @cache.read("foo")
-      @peek.write("foo", "bar")
-      assert_nil @cache.read("foo")
+      assert @cache.write(key, nil)
+      assert_nil @cache.read(key)
+      @peek.write(key, value)
+      assert_nil @cache.read(key)
     end
   end
 
   def test_local_cache_of_write_with_unless_exist
+    key = SecureRandom.uuid
+    value = SecureRandom.alphanumeric
     @cache.with_local_cache do
-      @cache.write("foo", "bar")
-      @cache.write("foo", "baz", unless_exist: true)
-      assert_equal @peek.read("foo"), @cache.read("foo")
+      @cache.write(key, value)
+      @cache.write(key, SecureRandom.alphanumeric, unless_exist: true)
+      assert_equal @peek.read(key), @cache.read(key)
     end
   end
 
   def test_local_cache_of_delete
+    key = SecureRandom.uuid
     @cache.with_local_cache do
-      @cache.write("foo", "bar")
-      @cache.delete("foo")
-      assert_nil @cache.read("foo")
+      @cache.write(key, SecureRandom.alphanumeric)
+      @cache.delete(key)
+      assert_nil @cache.read(key)
     end
   end
 
@@ -126,94 +149,112 @@ module LocalCacheBehavior
       skip
     end
 
+    prefix = SecureRandom.alphanumeric
+    key = "#{prefix}#{SecureRandom.uuid}"
+    other_key = "#{prefix}#{SecureRandom.uuid}"
+    third_key = SecureRandom.uuid
+    value = SecureRandom.alphanumeric
     @cache.with_local_cache do
-      @cache.write("foo", "bar")
-      @cache.write("fop", "bar")
-      @cache.write("bar", "foo")
-      @cache.delete_matched("fo*")
-      assert_not @cache.exist?("foo")
-      assert_not @cache.exist?("fop")
-      assert_equal "foo", @cache.read("bar")
+      @cache.write(key, SecureRandom.alphanumeric)
+      @cache.write(other_key, SecureRandom.alphanumeric)
+      @cache.write(third_key, value)
+      @cache.delete_matched("#{prefix}*")
+      assert_not @cache.exist?(key)
+      assert_not @cache.exist?(other_key)
+      assert_equal value, @cache.read(third_key)
     end
   end
 
   def test_local_cache_of_exist
+    key = SecureRandom.uuid
     @cache.with_local_cache do
-      @cache.write("foo", "bar")
-      @peek.delete("foo")
-      assert @cache.exist?("foo")
+      @cache.write(key, SecureRandom.alphanumeric)
+      @peek.delete(key)
+      assert @cache.exist?(key)
     end
   end
 
   def test_local_cache_of_increment
+    key = SecureRandom.uuid
     @cache.with_local_cache do
-      @cache.write("foo", 1, raw: true)
-      @peek.write("foo", 2, raw: true)
-      @cache.increment("foo")
+      @cache.write(key, 1, raw: true)
+      @peek.write(key, 2, raw: true)
+      @cache.increment(key)
 
-      expected = @peek.read("foo", raw: true)
+      expected = @peek.read(key, raw: true)
       assert_equal 3, Integer(expected)
-      assert_equal expected, @cache.read("foo", raw: true)
+      assert_equal expected, @cache.read(key, raw: true)
     end
   end
 
   def test_local_cache_of_decrement
+    key = SecureRandom.uuid
     @cache.with_local_cache do
-      @cache.write("foo", 1, raw: true)
-      @peek.write("foo", 3, raw: true)
+      @cache.write(key, 1, raw: true)
+      @peek.write(key, 3, raw: true)
 
-      @cache.decrement("foo")
-      expected = @peek.read("foo", raw: true)
+      @cache.decrement(key)
+      expected = @peek.read(key, raw: true)
       assert_equal 2, Integer(expected)
-      assert_equal expected, @cache.read("foo", raw: true)
+      assert_equal expected, @cache.read(key, raw: true)
     end
   end
 
   def test_local_cache_of_fetch_multi
+    key = SecureRandom.uuid
+    other_key = SecureRandom.uuid
     @cache.with_local_cache do
-      @cache.fetch_multi("foo", "bar") { |_key| true }
-      @peek.delete("foo")
-      @peek.delete("bar")
-      assert_equal true, @cache.read("foo")
-      assert_equal true, @cache.read("bar")
+      @cache.fetch_multi(key, other_key) { |_key| true }
+      @peek.delete(key)
+      @peek.delete(other_key)
+      assert_equal true, @cache.read(key)
+      assert_equal true, @cache.read(other_key)
     end
   end
 
   def test_local_cache_of_read_multi
+    key = SecureRandom.uuid
+    value = SecureRandom.alphanumeric
+    other_key = SecureRandom.uuid
+    other_value = SecureRandom.alphanumeric
     @cache.with_local_cache do
-      @cache.write("foo", "foo", raw: true)
-      @cache.write("bar", "bar", raw: true)
-      values = @cache.read_multi("foo", "bar", raw: true)
-      assert_equal "foo", @cache.read("foo", raw: true)
-      assert_equal "bar", @cache.read("bar", raw: true)
-      assert_equal "foo", values["foo"]
-      assert_equal "bar", values["bar"]
+      @cache.write(key, value, raw: true)
+      @cache.write(other_key, other_value, raw: true)
+      values = @cache.read_multi(key, other_key, raw: true)
+      assert_equal value, @cache.read(key, raw: true)
+      assert_equal other_value, @cache.read(other_key, raw: true)
+      assert_equal value, values[key]
+      assert_equal other_value, values[other_key]
     end
   end
 
   def test_initial_object_mutation_after_write
+    key = SecureRandom.uuid
     @cache.with_local_cache do
       initial = +"bar"
-      @cache.write("foo", initial)
+      @cache.write(key, initial)
       initial << "baz"
-      assert_equal "bar", @cache.read("foo")
+      assert_equal "bar", @cache.read(key)
     end
   end
 
   def test_initial_object_mutation_after_fetch
+    key = SecureRandom.uuid
     @cache.with_local_cache do
       initial = +"bar"
-      @cache.fetch("foo") { initial }
+      @cache.fetch(key) { initial }
       initial << "baz"
-      assert_equal "bar", @cache.read("foo")
-      assert_equal "bar", @cache.fetch("foo")
+      assert_equal "bar", @cache.read(key)
+      assert_equal "bar", @cache.fetch(key)
     end
   end
 
   def test_middleware
+    key = SecureRandom.uuid
+    value = SecureRandom.alphanumeric
     app = lambda { |env|
-      result = @cache.write("foo", "bar")
-      assert_equal "bar", @cache.read("foo") # make sure 'foo' was written
+      result = @cache.write(key, value)
+      assert_equal value, @cache.read(key) # make sure 'foo' was written
       assert result
       [200, {}, []]
     }
@@ -222,23 +263,27 @@ module LocalCacheBehavior
   end
 
   def test_local_race_condition_protection
+    key = SecureRandom.uuid
+    value = SecureRandom.alphanumeric
+    other_value = SecureRandom.alphanumeric
     @cache.with_local_cache do
       time = Time.now
-      @cache.write("foo", "bar", expires_in: 60)
+      @cache.write(key, value, expires_in: 60)
       Time.stub(:now, time + 61) do
-        result = @cache.fetch("foo", race_condition_ttl: 10) do
-          assert_equal "bar", @cache.read("foo")
-          "baz"
+        result = @cache.fetch(key, race_condition_ttl: 10) do
+          assert_equal value, @cache.read(key)
+          other_value
         end
-        assert_equal "baz", result
+        assert_equal other_value, result
       end
     end
   end
 
   def test_local_cache_should_read_and_write_false
+    key = SecureRandom.uuid
     @cache.with_local_cache do
-      assert @cache.write("foo", false)
-      assert_equal false, @cache.read("foo")
+      assert @cache.write(key, false)
+      assert_equal false, @cache.read(key)
     end
   end
 end
diff --git a/activesupport/test/cache/stores/mem_cache_store_test.rb b/activesupport/test/cache/stores/mem_cache_store_test.rb
index 377bdcdaf1..918318f8ae 100644
--- a/activesupport/test/cache/stores/mem_cache_store_test.rb
+++ b/activesupport/test/cache/stores/mem_cache_store_test.rb
@@ -79,9 +79,15 @@ class MemCacheStoreTest < ActiveSupport::TestCase
   # Overrides test from LocalCacheBehavior in order to stub out the cache clear
   # and replace it with a delete.
   def test_clear_also_clears_local_cache
-    key = "#{@namespace}:foo"
+    key = SecureRandom.uuid
+    cache = lookup_store(raw: true)
     client.stub(:flush_all, -> { client.delete(key) }) do
-      super
+      cache.with_local_cache do
+        cache.write(key, SecureRandom.alphanumeric)
+        cache.clear
+        assert_nil cache.read(key)
+      end
+      assert_nil cache.read(key)
     end
   end