crates_io_test_db: Add README.md

Author: Turbo87

crates/crates_io_test_db/README.md

@@ -0,0 +1,15 @@
+# crates_io_test_db
+
+This package contains the code necessary to create test databases for testing
+purposes.
+
+`TestDatabase::new()` can be used to create a new test database, based on a
+template database, which is lazily created the first time it is needed.
+
+The databases are created based on the `TEST_DATABASE_URL` environment variable,
+which should be set to a valid database URL. The template database will then be
+created with a similar name and `_template` suffix, while the test databases
+will use random suffixes.
+
+Note that the template database will be created with applied database migrations,
+so if you need an empty database, this is not the right tool for you.

crates/crates_io_test_db/src/lib.rs

@@ -1,3 +1,5 @@
+#![doc = include_str!("../README.md")]
+
 use crates_io_env_vars::required_var_parsed;
 use diesel::prelude::*;
 use diesel::r2d2::{ConnectionManager, Pool, PooledConnection};