I was generally aware of how relevant code reviews are for the development process in terms of ensuring certain programming conventions in the team, transferring knowledge from more experienced to less experienced programmers and spotting defects early.

Yet I did not know how code reviews compare with other software quality procedures such as testing.

A study found that code reading detected about 80 percent more faults
than testing. Another organization found that it cost six times as
much to detect design defects by using testing as by using inspections

My assumption was always that code reviews seemed expensive (time-wise) and that testing was the deal-maker of software quality. Apparently I was wrong.

Code reviews are cheaper than testing. And higher than average quality is only ensured when a multitude of measures are used among which: code reading, automated testing, prototyping, usability tests, etc. Only using all these techniques we are able to achieve defect-removal efficiencies on the order of 95 percent or higher.

P.S. I stumbled upon this while reading Code Complete 2