src/vs/workbench/api/common/extHostTask.ts/is
	export function is(value: tasks.IShellExecutionDTO | tasks.IProcessExecutionDTO | tasks.ICustomExecutionDTO | undefined): value is tasks.ICustomExecutionDTO {
		if (value) {
			const candidate = value as tasks.ICustomExecutionDTO;
			return candidate && candidate.customExecution === 'customExecution';
		} else {
			return false;
		}
	}