Slightly improve test layer setup by invoking the CrateLayer at runtime

This is the foundation to improve the situation later by adding support
for running CrateDB through Docker or other means.

Author: amotl

src/crate/client/tests.py

@@ -108,17 +108,23 @@ def setUpMocked(test):
 crate_port = 44209
 crate_transport_port = 44309
 local = '127.0.0.1'
-crate_layer = CrateLayer('crate',
-                         crate_home=crate_path(),
-                         port=crate_port,
-                         host=local,
-                         transport_port=crate_transport_port,
-                         settings=settings)
-
 crate_host = "{host}:{port}".format(host=local, port=crate_port)
 crate_uri = "http://%s" % crate_host
 
 
+def ensure_cratedb_layer():
+    global crate_layer
+
+    if crate_layer is None:
+        crate_layer = CrateLayer('crate',
+                                 crate_home=crate_path(),
+                                 port=crate_port,
+                                 host=local,
+                                 transport_port=crate_transport_port,
+                                 settings=settings)
+    return crate_layer
+
+
 def refresh(table):
     with connect(crate_host) as conn:
         cursor = conn.cursor()
@@ -348,7 +354,7 @@ def test_suite():
         optionflags=flags,
         encoding='utf-8'
     )
-    s.layer = crate_layer
+    s.layer = ensure_cratedb_layer()
     suite.addTest(s)
 
     s = doctest.DocFileSuite(
@@ -362,7 +368,7 @@ def test_suite():
         optionflags=flags,
         encoding='utf-8'
     )
-    s.layer = crate_layer
+    s.layer = ensure_cratedb_layer()
     suite.addTest(s)
 
     s = doctest.DocFileSuite(
@@ -372,7 +378,7 @@ def test_suite():
         optionflags=flags,
         encoding='utf-8'
     )
-    s.layer = crate_layer
+    s.layer = ensure_cratedb_layer()
     suite.addTest(s)
 
     return suite