tests: print diffs on test failures

Author: djc

Cargo.lock

@@ -37,7 +37,7 @@ otel = [
 ]
 
 # Exports code dependent on private interfaces for the integration test suite
-test = ["dep:walkdir"]
+test = ["dep:similar-asserts", "dep:walkdir"]
 
 # Sorted by alphabetic order
 [dependencies]
@@ -77,6 +77,7 @@ semver = "1.0"
 serde = { version = "1.0", features = ["derive"] }
 sha2 = "0.10"
 sharded-slab = "0.1.1"
+similar-asserts = { version = "1.7", optional = true } # test-only
 strsim = "0.11"
 tar = "0.4.26"
 tempfile = "3.8"

Cargo.toml

@@ -18,6 +18,7 @@ use std::{
 };
 
 use enum_map::{Enum, EnumMap, enum_map};
+use similar_asserts::SimpleDiff;
 use tempfile::TempDir;
 use url::Url;
 
@@ -236,12 +237,14 @@ impl Config {
         let out = self.run(args[0], &args[1..], env).await;
         if !out.ok || out.stdout != stdout || out.stderr != stderr {
             print_command(args, &out);
-            println!("expected.ok: true");
-            print_indented("expected.stdout", stdout);
-            print_indented("expected.stderr", stderr);
-            dbg!(out.stdout == stdout);
-            dbg!(out.stderr == stderr);
-            panic!();
+            print_diff(stdout, &out.stdout);
+            print_diff(stderr, &out.stderr);
+            panic!(
+                "expected OK, differences found: ok = {}, stdout = {}, stderr = {}",
+                out.ok,
+                out.stdout == stdout,
+                out.stderr == stderr
+            );
         }
     }
 
@@ -250,18 +253,14 @@ impl Config {
         let out = self.run(args[0], &args[1..], &[]).await;
         if out.ok || out.stdout != stdout || out.stderr != stderr {
             print_command(args, &out);
-            println!("expected.ok: false");
-            print_indented("expected.stdout", stdout);
-            print_indented("expected.stderr", stderr);
-            if out.ok {
-                panic!("expected command to fail");
-            } else if out.stdout != stdout {
-                panic!("expected stdout to match");
-            } else if out.stderr != stderr {
-                panic!("expected stderr to match");
-            } else {
-                unreachable!()
-            }
+            print_diff(stdout, &out.stdout);
+            print_diff(stderr, &out.stderr);
+            panic!(
+                "expected error, differences found: ok = {}, stdout = {}, stderr = {}",
+                out.ok,
+                out.stdout == stdout,
+                out.stderr == stderr
+            );
         }
     }
 
@@ -430,6 +429,17 @@ impl Config {
     }
 }
 
+fn print_diff(expected: &str, actual: &str) {
+    if expected == actual {
+        return;
+    }
+
+    println!(
+        "{}",
+        SimpleDiff::from_str(expected, actual, "expected", "actual")
+    );
+}
+
 // Describes all the features of the mock dist server.
 // Building the mock server is slow, so use simple scenario when possible.
 #[derive(Copy, Clone, Debug, Eq, PartialEq, Enum)]