Update test envvar and docs

README.md

@@ -6,3 +6,31 @@
 Package pgconn is a low-level PostgreSQL database driver.
 
 It is intended to serve as the foundation for the next generation of https://github.com/jackc/pgx.
+
+## Testing
+
+pgconn tests need a PostgreSQL database. It will connect to the database specified in the `PGX_TEST_CONN_STRING`
+environment variable. The `PGX_TEST_CONN_STRING` environment variable can be a URL or DSN. In addition, the standard `PG*`
+environment variables will be respected. Consider using [direnv](https://github.com/direnv/direnv) to simplify
+environment variable handling.
+
+### Example Test Environment
+
+Connect to your PostgreSQL server and run:
+
+```
+create database pgx_test;
+```
+
+Now you can run the tests:
+
+```
+PGX_TEST_CONN_STRING="host=/var/run/postgresql database=pgx_test" go test ./...
+```
+
+### Connection and Authentication Tests
+
+There are multiple connection types and means of authentication that pgconn supports. These tests are optional. They
+will only run if the appropriate environment variable is set. Run `go test -v | grep SKIP` to see if any tests are being
+skipped. Typical developers will not need to enable these tests. See travis.yml for example setup if you need change
+authentication code.