diff --git a/src/tests/config.rs b/src/tests/config.rs
index 1ed71b66..1f36998b 100644
--- a/src/tests/config.rs
+++ b/src/tests/config.rs
@@ -11,7 +11,7 @@ fn mutually_exclusive_set_options() {
     let (rc, out, err) = Nitrocli::new().run(&["config", "set", option1, option2]);
 
     assert_ne!(rc, 0);
-    assert_eq!(out, b"");
+    assert_eq!(out, b"", "{}", String::from_utf8_lossy(&out));
 
     let err = String::from_utf8(err).unwrap();
     assert!(err.contains("cannot be used with"), "{}", err);
diff --git a/src/tests/otp.rs b/src/tests/otp.rs
index 45ae7843..a87a8653 100644
--- a/src/tests/otp.rs
+++ b/src/tests/otp.rs
@@ -14,8 +14,13 @@ fn set_invalid_slot_raw(model: nitrokey::Model) {
     .run(&["otp", "set", "100", "name", "1234", "-f", "hex"]);
 
   assert_ne!(rc, 0);
-  assert_eq!(out, b"");
-  assert_eq!(&err[..24], b"Failed to write OTP slot");
+  assert_eq!(out, b"", "{}", String::from_utf8_lossy(&out));
+  assert_eq!(
+    &err[..24],
+    b"Failed to write OTP slot",
+    "{}",
+    String::from_utf8_lossy(&out)
+  );
 }
 
 #[test_device]
diff --git a/src/tests/run.rs b/src/tests/run.rs
index afa2128a..81ac9706 100644
--- a/src/tests/run.rs
+++ b/src/tests/run.rs
@@ -21,7 +21,7 @@ fn no_command_or_option() {
   let (rc, out, err) = Nitrocli::new().run(&[]);
 
   assert_ne!(rc, 0);
-  assert_eq!(out, b"");
+  assert_eq!(out, b"", "{}", String::from_utf8_lossy(&out));
 
   let s = String::from_utf8_lossy(&err).into_owned();
   assert!(s.starts_with("nitrocli"), "{}", s);
@@ -37,7 +37,7 @@ fn help_options() {
     let (rc, out, err) = Nitrocli::new().run(&all);
 
     assert_eq!(rc, 0);
-    assert_eq!(err, b"");
+    assert_eq!(err, b"", "{}", String::from_utf8_lossy(&err));
 
     let s = String::from_utf8_lossy(&out).into_owned();
     let mut args = args.to_vec();
@@ -93,7 +93,7 @@ fn version_option() {
     let (rc, out, err) = Nitrocli::new().run(&[opt]);
 
     assert_eq!(rc, 0);
-    assert_eq!(err, b"");
+    assert_eq!(err, b"", "{}", String::from_utf8_lossy(&err));
 
     let s = String::from_utf8_lossy(&out).into_owned();
     let _ = re;
@@ -346,8 +346,8 @@ sys.exit(42);
 
   let (rc, out, err) = ncli.run(&["ext"]);
   assert_eq!(rc, 42);
-  assert_eq!(out, b"");
-  assert_eq!(err, b"");
+  assert_eq!(out, b"", "{}", String::from_utf8_lossy(&out));
+  assert_eq!(err, b"", "{}", String::from_utf8_lossy(&out));
   Ok(())
 }
 
diff --git a/src/tests/status.rs b/src/tests/status.rs
index 1c90a722..7df70cb2 100644
--- a/src/tests/status.rs
+++ b/src/tests/status.rs
@@ -10,8 +10,13 @@ fn not_found_raw() {
   let (rc, out, err) = Nitrocli::new().run(&["status"]);
 
   assert_ne!(rc, 0);
-  assert_eq!(out, b"");
-  assert_eq!(err, b"Nitrokey device not found\n");
+  assert_eq!(out, b"", "{}", String::from_utf8_lossy(&out));
+  assert_eq!(
+    err,
+    b"Nitrokey device not found\n",
+    "{}",
+    String::from_utf8_lossy(&err)
+  );
 }
 
 #[test_device]