initial config for multi db tests

.travis.yml

@@ -5,15 +5,28 @@ dist: xenial
 cache: pip
 
 python:
-    - "3.6"
-    - "3.7"
-    - "3.8"
+  - "3.6"
+  - "3.7"
+  - "3.8"
+
+env:
+  - TEST_DATABASE_URLS="postgresql://localhost/test_database, mysql://localhost/test_database, sqlite:///test.db"
+
+services:
+  - postgresql
+  - mysql
+
 
 install:
-    - pip install -U -r requirements.txt
+  - pip install -U -r requirements.txt
+
+before_script:
+  - psql -c 'create database test_database;' -U postgres
+  - echo 'create database test_database;' | mysql
+
 
 script:
-    - scripts/test.sh
+  - scripts/test.sh
 
 after_script:
-    - codecov
+  - codecov