Covid-19 is testing companies’ balance sheet strength like nothing before. Specifically, it’s testing how much ready cash they have lying around, and the capacity to repay debt. On first glance, CarTrawler’s balance sheet looks pretty robust and resilient. It has no debt and €82 million in cash. However, dig a little through its corporate structure and you find just where the debt is located – and just how big a debt pile it actually is. When BC Partners and Insight Venture Partners bought the business in 2014, they set up a sister company, Mustang Midco, which issued €233 million of…