diff --git a/src/shared/tests.h b/src/shared/tests.h
index 7641b446b0..d7c9250487 100644
--- a/src/shared/tests.h
+++ b/src/shared/tests.h
@@ -177,7 +177,8 @@ _noreturn_ void log_test_failed_internal(const char *file, int line, const char
         ({                                                                                                              \
                 typeof(expr) _result = (expr);                                                                          \
                 if (_result < 0)                                                                                        \
-                        log_test_failed("Expected \"%s\" to succeed, but got error: %s", #expr, STRERROR(_result));     \
+                        log_test_failed("Expected \"%s\" to succeed, but got error: %"PRIiMAX"/%s",                     \
+                                        #expr, (intmax_t) _result, STRERROR(_result));                                  \
          })
 #endif
 
@@ -189,7 +190,8 @@ _noreturn_ void log_test_failed_internal(const char *file, int line, const char
         ({                                                                                                              \
                 typeof(expr) _result = (expr);                                                                          \
                 if (_result < 0)                                                                                        \
-                        log_test_failed("Expected \"%s\" to succeed, but got error: %s", #expr, STRERROR(_result));     \
+                        log_test_failed("Expected \"%s\" to succeed, but got error: %"PRIiMAX"/%s",                     \
+                                        #expr, (intmax_t) _result, STRERROR(_result));                                  \
                 if (_result == 0)                                                                                       \
                         log_test_failed("Expected \"%s\" to be positive, but it is zero.", #expr);                      \
          })
@@ -202,7 +204,8 @@ _noreturn_ void log_test_failed_internal(const char *file, int line, const char
         ({                                                                                                              \
                 typeof(expr) _result = (expr);                                                                          \
                 if (_result < 0)                                                                                        \
-                        log_test_failed("Expected \"%s\" to succeed, but got error: %s", #expr, STRERROR(_result));     \
+                        log_test_failed("Expected \"%s\" to succeed, but got error: %"PRIiMAX"/%s",                     \
+                                        #expr, (intmax_t) _result, STRERROR(_result));                                  \
                 if (_result != 0)                                                                                       \
                         log_test_failed("Expected \"%s\" to be zero, but it is %"PRIiMAX".",                            \
                                         #expr, (intmax_t) _result);                                                     \
@@ -217,13 +220,15 @@ _noreturn_ void log_test_failed_internal(const char *file, int line, const char
                 typeof(expr1) _expr1 = (expr1);                                                                         \
                 typeof(expr2) _expr2 = (expr2);                                                                         \
                 if (_expr1 < 0)                                                                                         \
-                        log_test_failed("Expected \"%s\" to succeed, but got error: %s", #expr1, STRERROR(_expr1));     \
+                        log_test_failed("Expected \"%s\" to succeed, but got error: %"PRIiMAX"/%s",                     \
+                                        #expr1, (intmax_t) _expr1, STRERROR(_expr1));                                   \
                 if (_expr1 != _expr2)                                                                                   \
                         log_test_failed("Expected \"%s == %s\", got %"PRIiMAX" != %"PRIiMAX,                            \
                                         #expr1, #expr2, (intmax_t) _expr1, (intmax_t) _expr2);                          \
         })
 #endif
 
+/* For functions that return a boolean on success and set errno on failure. */
 #ifdef __COVERITY__
 #  define ASSERT_OK_ERRNO(expr) __coverity_check__((expr) >= 0)
 #else
@@ -231,7 +236,8 @@ _noreturn_ void log_test_failed_internal(const char *file, int line, const char
         ({                                                                                                              \
                 typeof(expr) _result = (expr);                                                                          \
                 if (_result < 0)                                                                                        \
-                        log_test_failed("Expected \"%s\" to succeed, but got error: %s", #expr, STRERROR(errno));       \
+                        log_test_failed("Expected \"%s\" to succeed, but got errno: %d/%s",                             \
+                                        #expr, errno, STRERROR(errno));                                                 \
         })
 #endif
 
@@ -242,7 +248,8 @@ _noreturn_ void log_test_failed_internal(const char *file, int line, const char
         ({                                                                                                              \
                 typeof(expr) _result = (expr);                                                                          \
                 if (_result < 0)                                                                                        \
-                        log_test_failed("Expected \"%s\" to succeed, but got error: %s", #expr, STRERROR(errno));       \
+                        log_test_failed("Expected \"%s\" to succeed, but got errno: %d/%s",                             \
+                                        #expr, errno, STRERROR(errno));                                                 \
                 if (_result != 0)                                                                                       \
                         log_test_failed("Expected \"%s\" to be zero, but it is %"PRIiMAX".",                            \
                                         #expr, (intmax_t) _result);                                                     \
@@ -257,7 +264,8 @@ _noreturn_ void log_test_failed_internal(const char *file, int line, const char
                 typeof(expr1) _expr1 = (expr1);                                                                         \
                 typeof(expr2) _expr2 = (expr2);                                                                         \
                 if (_expr1 < 0)                                                                                         \
-                        log_test_failed("Expected \"%s\" to succeed, but got error: %s", #expr1, STRERROR(errno));      \
+                        log_test_failed("Expected \"%s\" to succeed, but got errno: %d/%s",                             \
+                                        #expr1, errno, STRERROR(errno));                                                \
                 if (_expr1 != _expr2)                                                                                   \
                         log_test_failed("Expected \"%s == %s\", but %"PRIiMAX" != %"PRIiMAX,                            \
                                         #expr1, #expr2, (intmax_t) _expr1, (intmax_t) _expr2);                          \
@@ -283,11 +291,11 @@ _noreturn_ void log_test_failed_internal(const char *file, int line, const char
                 int _expr1 = (expr1);                                                                                   \
                 int _expr2 = (expr2);                                                                                   \
                 if (_expr1 >= 0)                                                                                        \
-                        log_test_failed("Expected \"%s\" to fail with error \"%s\", but it succeeded",                  \
-                                        #expr1, STRERROR(_expr2));                                                      \
+                        log_test_failed("Expected \"%s\" to fail with error %d/\"%s\", but it succeeded",               \
+                                        #expr1, -_expr2, STRERROR(_expr2));                                             \
                 else if (-_expr1 != _expr2)                                                                             \
-                        log_test_failed("Expected \"%s\" to fail with error \"%s\", but got the following error: %s",   \
-                                        #expr1, STRERROR(_expr2), STRERROR(_expr1));                                    \
+                        log_test_failed("Expected \"%s\" to fail with error %d/\"%s\", but got the following error: %d/%s", \
+                                        #expr1, -_expr2, STRERROR(_expr2), _expr1, STRERROR(_expr1));                   \
         })
 #endif
 
@@ -299,11 +307,11 @@ _noreturn_ void log_test_failed_internal(const char *file, int line, const char
                 int _expr1 = (expr1);                                                                                   \
                 int _expr2 = (expr2);                                                                                   \
                 if (_expr1 >= 0)                                                                                        \
-                        log_test_failed("Expected \"%s\" to fail with error \"%s\", but it succeeded",                  \
-                                        #expr1, STRERROR(_expr2));                                                      \
+                        log_test_failed("Expected \"%s\" to fail with errno %d/\"%s\", but it succeeded",               \
+                                        #expr1, _expr2, STRERROR(_expr2));                                              \
                 else if (errno != _expr2)                                                                               \
-                        log_test_failed("Expected \"%s\" to fail with error \"%s\", but got the following error: %s",   \
-                                        #expr1, STRERROR(_expr2), STRERROR(errno));                                     \
+                        log_test_failed("Expected \"%s\" to fail with errno %d/\"%s\", but got the following errno: %d/%s", \
+                                        #expr1, _expr2, STRERROR(_expr2), errno, STRERROR(errno));                      \
         })
 #endif