Add integration tests for group_by precedence.

Test that, when a group is created with group_by, variables from the
corresponding group_vars/ file are correctly pulled in, and override
variables specified in group_vars/all.

See ansible/ansible#8664.

test/integration/targets/group_by/group_vars/camelus

@@ -0,0 +1 @@
+dos: 'two'

test/integration/targets/group_by/group_vars/vicugna

@@ -0,0 +1 @@
+tres: 'three'

test/integration/targets/group_by/inventory.group_by

@@ -1,3 +1,6 @@
+# ungrouped
+camel genus=camelus ansible_connection=local
+
 [lamini]
 alpaca genus=vicugna
 llama genus=lama

test/integration/targets/group_by/test_group_by.yml

@@ -17,7 +17,7 @@
 # along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
 
 - name: Create overall groups
-  hosts: lamini
+  hosts: all
   gather_facts: false
   tasks:
     - debug: var=genus
@@ -51,6 +51,15 @@
     - name: set a fact to check that we ran this play
       set_fact: genus_lama=true
 
+- name: Camelus group validation
+  hosts: camelus
+  gather_facts: false
+  tasks:
+    - name: verify that only the camel is in this group
+      assert: { that: "inventory_hostname == 'camel'" }
+    - name: set a fact to check that we ran this play
+      set_fact: genus_camelus=true
+
 - name: Vic group validation
   hosts: vic
   gather_facts: false
@@ -69,6 +78,15 @@
     - name: set a fact to check that we ran this play
       set_fact: genus_lam=true
 
+- name: Cam group validation
+  hosts: cam
+  gather_facts: false
+  tasks:
+    - name: verify that only the camel is in this group
+      assert: { that: "inventory_hostname == 'camel'" }
+    - name: set a fact to check that we ran this play
+      set_fact: genus_cam=true
+
 - name: Vi group validation
   hosts: vi
   gather_facts: false
@@ -87,6 +105,15 @@
     - name: set a fact to check that we ran this play
       set_fact: genus_la=true
 
+- name: Ca group validation
+  hosts: ca
+  gather_facts: false
+  tasks:
+    - name: verify that only the camel is in this group
+      assert: { that: "inventory_hostname == 'camel'" }
+    - name: set a fact to check that we ran this play
+      set_fact: genus_ca=true
+
 - name: VICUGNA group validation
   hosts: VICUGNA
   gather_facts: false
@@ -105,6 +132,15 @@
     - name: set a fact to check that we ran this play
       set_fact: genus_LAMA=true
 
+- name: CAMELUS group validation
+  hosts: CAMELUS
+  gather_facts: false
+  tasks:
+    - name: verify that only the camel is in this group
+      assert: { that: "inventory_hostname == 'camel'" }
+    - name: set a fact to check that we ran this play
+      set_fact: genus_CAMELUS=true
+
 - name: genus group validation (expect skipped)
   hosts: 'genus'
   gather_facts: false
@@ -125,3 +161,27 @@
   tasks:
     - name: check that llama matched all four groups
       assert: { that: ["genus_lama", "genus_lam", "genus_la", "genus_LAMA"] }
+
+- hosts: camel
+  gather_facts: false
+  tasks:
+    - name: check that camel matched all four groups
+      assert: { that: ["genus_camelus", "genus_cam", "genus_ca", "genus_CAMELUS"] }
+
+- hosts: vicugna
+  gather_facts: false
+  tasks:
+    - name: check group_vars variable overrides for vicugna
+      assert: { that: ["uno == 1", "dos == 2", "tres == 'three'"] }
+
+- hosts: lama
+  gather_facts: false
+  tasks:
+    - name: check group_vars variable overrides for lama
+      assert: { that: ["uno == 1", "dos == 2", "tres == 3"] }
+
+- hosts: camelus
+  gather_facts: false
+  tasks:
+    - name: check group_vars variable overrides for camelus
+      assert: { that: ["uno == 1", "dos == 'two'", "tres == 3"] }