With gas piping it’s primarily the unions (a large nut like connector) that leaks. Pipe connections on black iron (steel) pipe can leak, but it is less common, they are a threaded connector joining straight pipes, right angles and T-shaped connectors.
Gas pipe connections are most commonly sealed with pipe dope (a paste) and sometimes with Teflon tape (pink for gas) Flexible CSST gas lines have a lot less connectors which dramatically reduces the likelihood for potential leaks.
If you have kids get a bottle of their “bubble juice”, apply it to the suspected area with a spray bottle or paint brush and look for bubbles after a few seconds or up to a good minute for a very slow leak.
If its propane the shutoff is located at the tank and easily turned off by hand.
NOTE: We offer optional gas leak testing with our home inspections.