Set additional env var for custom postgres db

Author: mchwalek

postgres/lib/testcontainers/postgres.rb

@@ -103,6 +103,7 @@ def with_password(password)
 
     def _configure
       add_env("POSTGRES_DATABASE", @database)
+      add_env("POSTGRES_DB", @database)
       add_env("POSTGRES_USER", @username)
 
       raise ContainerLaunchException, "Password is required for non-root users" if @password.nil? || @password.empty?

postgres/test/postgres_container_test.rb

@@ -37,6 +37,7 @@ def test_it_returns_the_default_port
 
   def test_it_is_configured_with_the_default_environment_variables
     assert "test", @container.get_env("POSTGRES_DATABASE")
+    assert "test", @container.get_env("POSTGRES_DB")
     assert "test", @container.get_env("POSTGRES_USER")
     assert "test", @container.get_env("POSTGRES_PASSWORD")
     assert "test", @container.get_env("POSTGRES_ROOT_PASSWORD")