tests/runner.rs: use pretty-assertions crate

The workflow here involves looking for differences in output from
the test programs between us and openssl.  That is not very
friendly because rust's default Debug format escapes newlines.  Add
a newtype for `Output` which doesn't do that.

Author: ctz

Cargo.lock

@@ -15,3 +15,6 @@ log = "0.4"
 openssl-probe = "0.1"
 openssl-sys = "0.9"
 rustls = "0.23.27"
+
+[dev-dependencies]
+pretty_assertions = "1"

Cargo.toml

@@ -1,8 +1,10 @@
 use std::io::Read;
-use std::ops::Add;
+use std::ops::{Add, Deref};
 use std::process::{Child, Command, Output, Stdio};
 use std::sync::atomic;
-use std::{fs, net, thread, time};
+use std::{fmt, fs, net, thread, time};
+
+use pretty_assertions::assert_eq;
 
 /* Note:
  *
@@ -807,17 +809,42 @@ impl Drop for KillOnDrop {
     }
 }
 
-fn print_output(out: Output) -> Output {
-    println!("status: {:?}\n", out.status);
-    println!(
-        "stdout:\n{}\n",
-        String::from_utf8(out.stdout.clone()).unwrap()
-    );
-    println!(
-        "stderr:\n{}\n",
-        String::from_utf8(out.stderr.clone()).unwrap()
-    );
-    out
+fn print_output(out: Output) -> PrettyOutput {
+    let p = PrettyOutput(out);
+    println!("output: {p:?}");
+    p
+}
+
+#[derive(PartialEq)]
+struct PrettyOutput(Output);
+
+impl fmt::Debug for PrettyOutput {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Output")
+            .field("status", &self.0.status)
+            .field("stdout", &"<follows>")
+            .field("stderr", &"<follows>")
+            .finish()?;
+
+        // ensure line endings in command output appear literally, so
+        // pretty_assertions can make a nice diff.
+        writeln!(f)?;
+        for l in String::from_utf8(self.0.stdout.clone()).unwrap().lines() {
+            writeln!(f, "stdout => {l}")?;
+        }
+        for l in String::from_utf8(self.0.stderr.clone()).unwrap().lines() {
+            writeln!(f, "stderr => {l}")?;
+        }
+        Ok(())
+    }
+}
+
+impl Deref for PrettyOutput {
+    type Target = Output;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
 }
 
 /// Wait until we can connect to localhost:port.