feat(cli): read connection parameters from environment variables

Add missing variables for user and database name.

README.md

@@ -14,6 +14,10 @@ Create a connection to a PostgreSQL database.
 
 Defaults to the `postgres` database on `localhost` with the `postgres` user.
 Pass alternate connection parameters as options.
+You can save yourself some typing by setting the environment variables `PGDATABASE`, 
+`PGHOST`, `PGPORT` and/or `PGUSER` to appropriate values.
+It is also convenient to have a [.pgpass](https://www.postgresql.org/docs/current/libpq-pgpass.html) file 
+to avoid regularly having to type in passwords.
 
 #### Options
 

heave/cli.py

@@ -77,8 +77,15 @@ def connect(
     "--username",
     default="",
     help="Username to connect to the postgres database.",
+    envvar="PGUSER",
+)
+@click.option(
+    "-d",
+    "--dbname",
+    default="postgres",
+    help="Database name to connect to.",
+    envvar="PGDATABASE",
 )
-@click.option("-d", "--dbname", default="postgres", help="Database name to connect to.")
 @click.pass_context
 def cli(
     ctx,

tests/test_cli.py

@@ -78,10 +78,23 @@ def test_connection(self, runner, monkeypatch):
         mock_connect = Mock()
         monkeypatch.setattr("heave.cli.connect", mock_connect)
         runner.invoke(cli, ["insert"])
-        assert mock_connect.called_with(
+        mock_connect.assert_called_with(
             ANY, "postgresql", "postgres", "localhost", "5432", "", "psycopg"
         )
 
+    def test_connection_envvars(self, runner, monkeypatch):
+        """Test the connection parameters from environment variables."""
+        mock_connect = Mock()
+        monkeypatch.setattr("heave.cli.connect", mock_connect)
+        monkeypatch.setenv("PGHOST", "myhost")
+        monkeypatch.setenv("PGPORT", "1234")
+        monkeypatch.setenv("PGUSER", "myuser")
+        monkeypatch.setenv("PGDATABASE", "mydb")
+        runner.invoke(cli, ["insert"])
+        mock_connect.assert_called_with(
+            ANY, "postgresql", "mydb", "myhost", "1234", "myuser", "psycopg"
+        )
+
     def test_insert(self, runner, monkeypatch):
         """Test the insert command."""
         data = Table(