2 files changed, 52 insertions, 3 deletions
diff --git a/lib/error_handler.c b/lib/error_handler.c
index 4e06919..cb2ef51 100644
--- a/lib/error_handler.c
+++ b/lib/error_handler.c
@@ -16,13 +16,19 @@ const char *SPM_ERR_STRING[] = {
         NULL,
 };
 
+/**
+ * Append error text to an existing spmerrno error string
+ * @param reason message text
+ */
 void spmerrno_cause(const char *reason) {
     char *buf = spmerrbuf_reason;
-    sprintf(buf, " (%s)", reason);
-    return;
+    if (reason != NULL) {
+        sprintf(buf, " (%s)", reason);
+    }
 }
+
 /**
- *
+ * Translate a spmerrno code to an error string
  * @param code
  * @return
  */
diff --git a/tests/test_error_handler_spm_perror.c b/tests/test_error_handler_spm_perror.c
new file mode 100644
index 0000000..a8b55db
--- /dev/null
+++ b/tests/test_error_handler_spm_perror.c
@@ -0,0 +1,43 @@
+#include "spm.h"
+#include "framework.h"
+
+const char *testFmt = "case %s: returned '%s', expected '%s'\n";
+struct TestCase testCase[] = {
+        {.caseValue.sptr = "oh no it broke", .truthValue.sptr = "oh no it broke: No such file or directory", .arg[0].signed_integer = ENOENT},
+        {.caseValue.sptr = "kaboom", .truthValue.sptr = "kaboom: Failed to fetch package", .arg[0].signed_integer = SPM_ERR_PKG_FETCH},
+};
+size_t numCases = sizeof(testCase) / sizeof(struct TestCase);
+
+int main(int argc, char *argv[]) {
+    char *tty_path = NULL;
+    if ((tty_path = ttyname(STDERR_FILENO)) == NULL) {
+        perror("tty check");
+        return 0;
+    }
+
+    for (size_t i = 0; i < numCases; i++) {
+        char buf[BUFSIZ] = {0,};
+        char *buffer = buf;
+        int stderr_save = 0;
+
+        fflush(stderr);
+
+        // Redirect stdout
+        stderr_save = dup(STDERR_FILENO);
+        freopen("/dev/null", "w", stderr);
+        setvbuf(stderr, buffer, _IOLBF, sizeof(buf));
+
+        // Do test
+        spmerrno = testCase[i].arg[0].signed_integer;
+        spm_perror(testCase[i].caseValue.sptr);
+        fflush(stderr);
+
+        strip(buffer);
+
+        // Restore stderr
+        dup2(stderr_save, STDERR_FILENO);
+        setvbuf(stderr, NULL, _IONBF, 0);
+
+        myassert(strcmp(buffer, testCase[i].truthValue.sptr) == 0, testFmt, testCase[i].caseValue.sptr, buffer, testCase[i].truthValue.sptr);
+    }
+}