Add a test case using environment variables for connecting

spec/helpers.rb

@@ -606,6 +606,17 @@ def run_with_gate(timeout=10)
 			gate_stop(gate)
 		end
 	end
+
+	def with_env_vars(**kwargs)
+		kwargs = kwargs.map{|k,v| [k.to_s, v && v.to_s] }.to_h
+		old_values = ENV.slice(*kwargs.keys)
+		ENV.merge!(kwargs)
+		begin
+			yield
+		ensure
+			ENV.merge!(old_values)
+		end
+	end
 end
 
 

spec/pg/connection_spec.rb

@@ -318,6 +318,15 @@
 		tmpconn.finish
 	end
 
+	it "connects with envirinment variables" do
+		tmpconn = with_env_vars(PGHOST: "localhost", PGPORT: @port, PGDATABASE: "test") do
+			described_class.connect
+		end
+		expect( tmpconn.status ).to eq( PG::CONNECTION_OK )
+		expect( tmpconn.host ).to eq( "localhost" )
+		tmpconn.finish
+	end
+
 	it "connects using Hash with multiple hosts", :postgresql_12 do
 		tmpconn = described_class.connect( host: "#{@unix_socket}xx,127.0.0.1,localhost", port: @port, dbname: "test" )
 		expect( tmpconn.status ).to eq( PG::CONNECTION_OK )