fix(test): make test output consistent across OSes

src/lib.rs

@@ -1439,7 +1439,7 @@ to = "markdown"
         insta::assert_snapshot!(book, @r###"
         ├─ log output
         │  INFO mdbook::book: Running the pandoc backend    
-        │  WARN mdbook_pandoc::preprocess: Failed to resolve image link 'https://doesnotexist.fake/main.yml?style=flat-square' in chapter 'Some Chapter': could not fetch remote image: https://doesnotexist.fake/main.yml?style=flat-square: Dns Failed: resolve dns name 'doesnotexist.fake:443': failed to lookup address information: nodename nor servname provided, or not known    
+        │  WARN mdbook_pandoc::preprocess: Failed to resolve image link 'https://doesnotexist.fake/main.yml?style=flat-square' in chapter 'Some Chapter': could not fetch remote image: Dns Failed    
         │  WARN mdbook_pandoc::preprocess: Replacing image with description    
         │  INFO mdbook_pandoc::pandoc::renderer: Wrote output to book/markdown/book.md    
         ├─ markdown/book.md

src/preprocess.rs

@@ -77,7 +77,12 @@ struct UnresolvableRemoteImage {
 
 impl fmt::Display for UnresolvableRemoteImage {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "could not fetch remote image: {:#}", self.err)
+        if cfg!(test) {
+            // in tests, print less verbose error message to be consistent across operating systems
+            write!(f, "could not fetch remote image: {}", self.err.kind())
+        } else {
+            write!(f, "could not fetch remote image: {}", self.err)
+        }
     }
 }