Analyse following RPM build log snippet. Describe contents accurately, without speculation or suggestions for resolution.            
Your analysis must be as concise as possible, while keeping relevant information intact.
Snippet: 
Failures:
  1) MiniMagick::Shell#execute with open3 executes the command in the shell
     Failure/Error: expect(stderr).to match("unable to open image")
       expected "identify: no decode delegate for this image format `' @ error/constitute.c/ReadImage/746.\n" to match "unable to open image"
       Diff:
       @@ -1 +1 @@
       -unable to open image
       +identify: no decode delegate for this image format `' @ error/constitute.c/ReadImage/746.
     # ./spec/lib/mini_magick/shell_spec.rb:54:in 'block (5 levels) in <top (required)>'
     # /usr/share/gems/gems/webmock-3.23.1/lib/webmock/rspec.rb:39:in 'block (2 levels) in <top (required)>'
RSpec test failure causing the build failure.
The stderr output is caught into stderr variable and matched against "unable to open image", which is testing the underlying binary this library wraps. It changed the message which causes the test failure.