Fix DB renaming fixture for Multi-DB environment (#679)

For Django configurations using multiple databases, there's a subtle bug
that doesn't rename databases, if there's an SQLite one that triggers
the `return` statement in the existing feature.

As the return value doesn't seem to be used, we can just move to the
next iteration in the `for`-loop, and evaluate the following DB.

A test was added to consider this scenario.

Author: adamantike

pytest_django/fixtures.py

@@ -47,9 +47,9 @@ def django_db_modify_db_settings_xdist_suffix(request):
 
         if not test_name:
             if db_settings["ENGINE"] == "django.db.backends.sqlite3":
-                return ":memory:"
-            else:
-                test_name = "test_{}".format(db_settings["NAME"])
+                continue
+
+            test_name = "test_{}".format(db_settings["NAME"])
 
         # Put a suffix like _gw0, _gw1 etc on xdist processes
         xdist_suffix = getattr(request.config, "slaveinput", {}).get("slaveid")

tests/test_db_setup.py

@@ -215,6 +215,50 @@ def test_a():
         result.stdout.fnmatch_lines(["*PASSED*test_a*"])
 
 
+class TestSqliteWithMultipleDbsAndXdist:
+
+    db_settings = {
+        "default": {
+            "ENGINE": "django.db.backends.sqlite3",
+            "NAME": "/tmp/should-not-be-used",
+        },
+        "db2": {
+            "ENGINE": "django.db.backends.sqlite3",
+            "NAME": "db_name",
+            "TEST": {"NAME": "test_custom_db_name"},
+        }
+    }
+
+    def test_sqlite_database_renamed(self, django_testdir):
+        pytest.importorskip("xdist")
+
+        django_testdir.create_test_module(
+            """
+            import pytest
+            from django.db import connections
+
+            @pytest.mark.django_db
+            def test_a():
+                (conn_db2, conn_default) = sorted(
+                    connections.all(),
+                    key=lambda conn: conn.alias,
+                )
+
+                assert conn_default.vendor == 'sqlite'
+                db_name = conn_default.creation._get_test_db_name()
+                assert 'file:memorydb' in db_name
+
+                assert conn_db2.vendor == 'sqlite'
+                db_name = conn_db2.creation._get_test_db_name()
+                assert 'test_custom_db_name_gw' in db_name
+        """
+        )
+
+        result = django_testdir.runpytest_subprocess("--tb=short", "-vv", "-n1")
+        assert result.ret == 0
+        result.stdout.fnmatch_lines(["*PASSED*test_a*"])
+
+
 @pytest.mark.skipif(
     get_django_version() >= (1, 9),
     reason=(