Only test if we can use processes and it's not an in memory db

JRuby can't support processes, and in memory db can't support changing
the handlers/connections during the test.

activerecord/test/cases/query_cache_test.rb

@@ -95,66 +95,69 @@ class QueryCacheTest < ActiveRecord::TestCase
     ActiveRecord::Base.connection_handlers = { writing: ActiveRecord::Base.default_connection_handler }
   end
 
-  def test_query_cache_with_multiple_handlers_and_forked_processes
-    ActiveRecord::Base.connection_handlers = {
-      writing: ActiveRecord::Base.default_connection_handler,
-      reading: ActiveRecord::ConnectionAdapters::ConnectionHandler.new
-    }
 
-    ActiveRecord::Base.connected_to(role: :reading) do
-      ActiveRecord::Base.establish_connection(ActiveRecord::Base.configurations["arunit"])
-    end
+  if Process.respond_to?(:fork) && !in_memory_db?
+    def test_query_cache_with_multiple_handlers_and_forked_processes
+      ActiveRecord::Base.connection_handlers = {
+        writing: ActiveRecord::Base.default_connection_handler,
+        reading: ActiveRecord::ConnectionAdapters::ConnectionHandler.new
+      }
 
-    rd, wr = IO.pipe
-    rd.binmode
-    wr.binmode
+      ActiveRecord::Base.connected_to(role: :reading) do
+        ActiveRecord::Base.establish_connection(ActiveRecord::Base.configurations["arunit"])
+      end
 
-    pid = fork {
-      rd.close
-      status = 0
+      rd, wr = IO.pipe
+      rd.binmode
+      wr.binmode
 
-      middleware { |env|
-        begin
-          assert_cache :clean
+      pid = fork {
+        rd.close
+        status = 0
 
-          # first request dirties cache
-          ActiveRecord::Base.connected_to(role: :reading) do
-            Post.first
-            assert_cache :dirty
-          end
-
-          # should clear the cache
-          Post.create!(title: "a new post", body: "and a body")
-
-          # fails because cache is still dirty
-          ActiveRecord::Base.connected_to(role: :reading) do
+        middleware { |env|
+          begin
             assert_cache :clean
-            Post.first
-          end
 
-        rescue Minitest::Assertion => e
-          wr.write Marshal.dump e
-          status = 1
-        end
-      }.call({})
+            # first request dirties cache
+            ActiveRecord::Base.connected_to(role: :reading) do
+              Post.first
+              assert_cache :dirty
+            end
+
+            # should clear the cache
+            Post.create!(title: "a new post", body: "and a body")
+
+            # fails because cache is still dirty
+            ActiveRecord::Base.connected_to(role: :reading) do
+              assert_cache :clean
+              Post.first
+            end
+
+          rescue Minitest::Assertion => e
+            wr.write Marshal.dump e
+            status = 1
+          end
+        }.call({})
+
+        wr.close
+        exit!(status)
+      }
 
       wr.close
-      exit!(status)
-    }
 
-    wr.close
+      Process.waitpid pid
+      if !$?.success?
+        raise Marshal.load(rd.read)
+      else
+        assert_predicate $?, :success?
+      end
 
-    Process.waitpid pid
-    if !$?.success?
-      raise Marshal.load(rd.read)
-    else
-      assert_predicate $?, :success?
+      rd.close
+    ensure
+      ActiveRecord::Base.connection_handlers = { writing: ActiveRecord::Base.default_connection_handler }
     end
-
-    rd.close
-  ensure
-    ActiveRecord::Base.connection_handlers = { writing: ActiveRecord::Base.default_connection_handler }
-  end unless in_memory_db?
+  end
 
   def test_query_cache_across_threads
     with_temporary_connection_pool do