improve output of C tests

integration-tests/src/bindings_tests/mod.rs

@@ -1,14 +1,28 @@
+use std::fs;
+
+extern "C" {
+    // set up to send test output to TEST-OUTPUT
+    fn setup_output();
+    // close the output file
+    fn finish_output();
+}
+
 // Each suite is represented by a <name>_tests C function in <name>.c.
 // All of these C files are built into a library that is linked to the crate -- but not to test
 // crates.  So, this macro produces a "glue function" that calls the C function, and that can be
 // called from test crates.
 macro_rules! suite(
     { $s:ident } => {
-    pub fn $s() -> i32 {
+    pub fn $s() -> (i32, String) {
         extern "C" {
             fn $s() -> i32;
         }
-        unsafe { $s() }
+        unsafe { setup_output() };
+        let res = unsafe { $s() };
+        unsafe { finish_output() };
+        let output = fs::read_to_string("TEST-OUTPUT")
+            .unwrap_or_else(|e| format!("could not open TEST-OUTPUT: {}", e));
+        (res, output)
     }
     };
 );

integration-tests/src/bindings_tests/replica.c

@@ -1,8 +1,8 @@
 #include <stdlib.h>
 #include <sys/stat.h>
 #include <string.h>
-#include "unity.h"
 #include "taskchampion.h"
+#include "unity.h"
 
 // creating an in-memory replica does not crash
 static void test_replica_creation(void) {

integration-tests/src/bindings_tests/test.c

@@ -1,6 +1,30 @@
+#include <stdio.h>
 #include "unity.h"
 
 // these functions are shared between all test "suites"
 // and cannot be customized per-suite.
 void setUp(void) { }
 void tearDown(void) { }
+
+static FILE *output = NULL;
+
+// Set up for test_output, writing output to "TEST-OUTPUT" in the
+// current directory.  The Rust test harness reads this file to get
+// the output and display it only on failure.  This is called by
+// the Rust test harness
+void setup_output(void) {
+    output = fopen("TEST-OUTPUT", "w");
+}
+
+// Close the output file.  Called by the Rust test harness.
+void finish_output(void) {
+    fclose(output);
+    output = NULL;
+}
+
+// this replaces UNITY_OUTPUT_CHAR, and writes output to
+// TEST-OUTPUT in the current directory; the Rust test harness
+// will read this data if the test fails.
+void test_output(char c) {
+    fputc(c, output);
+}