Move miq_preloader_spec tree building logic to shared_context

This makes a new rspec shared_context that can be used to replicate the
tree building functionality in the specs that test the method
`MiqPreloader.polymorphic_preload_for_child_classes`.  The same data can
then be used in higher level abstraction tests to confirm the
functionality works as expected there as well.

spec/lib/miq_preloader_spec.rb

@@ -114,29 +114,12 @@ def preload_and_scope(*args)
   end
 
   describe ".polymorphic_preload_for_child_classes" do
+    include_context "simple ems_metadata tree" do
+      before { init_full_tree }
+    end
+
     it "preloads polymorphic relationships that are defined" do
-      ems         = FactoryGirl.create(:ems_infra)
-      clusters    = FactoryGirl.create_list(:ems_cluster, 2,
-                                            :ext_management_system => ems)
-      host_group1 = FactoryGirl.create_list(:host, 2,
-                                            :ext_management_system => ems,
-                                            :ems_cluster           => clusters.first)
-      host_group2 = FactoryGirl.create_list(:host, 2,
-                                            :ext_management_system => ems,
-                                            :ems_cluster           => clusters.last)
-
-      ems_rel      = ems.init_relationship
-      cluster_rels = clusters.map { |cluster| cluster.init_relationship(ems_rel) }
-      host_rels1   = host_group1.map { |host| [host, host.init_relationship(cluster_rels.first)] }
-      host_rels2   = host_group2.map { |host| [host, host.init_relationship(cluster_rels.last)] }
-
-      (host_rels1 + host_rels2).each do |(host, host_rel)|
-        FactoryGirl.create_list(:vm, 2, :ext_management_system => ems, :host => host).each do |vm|
-          vm.init_relationship(host_rel)
-        end
-      end
-
-      tree    = ExtManagementSystem.last.fulltree_rels_arranged(:except_type => "VmOrTemplate")
+      tree    = ems.fulltree_rels_arranged(:except_type => "VmOrTemplate")
       records = Relationship.flatten_arranged_rels(tree)
 
       hosts_scope   = Host.select(Host.arel_table[Arel.star], :v_total_vms)

spec/support/examples_group/shared_context_for_ems_metadata_tree.rb

@@ -0,0 +1,68 @@
+shared_context "simple ems_metadata tree" do
+  #####################
+  # Context Variables #
+  #####################
+
+  # These can be updated to increase the amount of data in the tree
+
+  let(:cluster_count)     { 2 }
+  let(:hosts_per_cluster) { 2 }
+  let(:vms_per_host)      { 2 }
+
+  ###############
+  # Base models #
+  ###############
+
+  let(:ems)      { FactoryGirl.create(:ems_infra) }
+  let(:clusters) { FactoryGirl.create_list(:ems_cluster, cluster_count, :ext_management_system => ems) }
+
+  let(:hosts) do
+    hosts = []
+    clusters.each do |cluster|
+      hosts += FactoryGirl.create_list(:host, hosts_per_cluster,
+                                       :ext_management_system => ems,
+                                       :ems_cluster           => cluster)
+    end
+    hosts
+  end
+
+  let(:vms) do
+    vms = []
+    hosts.each do |host|
+      vms += FactoryGirl.create_list(:vm, vms_per_host,
+                                     :ext_management_system => ems,
+                                     :host                  => host)
+    end
+    vms
+  end
+
+  #################
+  # Relationships #
+  #################
+
+  let(:ems_rel)      { ems.init_relationship }
+  let(:cluster_rels) { clusters.map { |cluster| cluster.init_relationship(ems_rel) } }
+
+  # The next to use a integer division trick to map the proper parent_rel to
+  # the record being created (the `[index / child_per_parent]` part)
+
+  let(:host_rels) do
+    hosts.map.with_index do |host, index|
+      host.init_relationship(cluster_rels[index / hosts_per_cluster])
+    end
+  end
+
+  let(:vm_rels) do
+    vms.map.with_index do |vm, index|
+      vm.init_relationship(host_rels[index / vms_per_host])
+    end
+  end
+
+  ###########
+  # Helpers #
+  ###########
+
+  # Convenience statement for initializing the tree (there is no included
+  # `before` to do this automatically
+  let(:init_full_tree) { vm_rels }
+end