serialize C integration tests

Cargo.lock

@@ -1529,6 +1529,7 @@ dependencies = [
  "anyhow",
  "cc",
  "env_logger 0.8.4",
+ "lazy_static",
  "log",
  "pretty_assertions",
  "taskchampion",

integration-tests/Cargo.toml

@@ -18,6 +18,7 @@ tempfile = "3"
 pretty_assertions = "1"
 log = "^0.4.14"
 env_logger = "^0.8.3"
+lazy_static = "1"
 
 [build-dependencies]
 cc = "1.0"

integration-tests/tests/bindings.rs

@@ -1,7 +1,17 @@
+use lazy_static::lazy_static;
+use std::sync::Mutex;
+
+lazy_static! {
+    // the C library running the tests is not reentrant, so we use a mutex to ensure that only one
+    // test runs at a time.
+    static ref MUTEX: Mutex<()> = Mutex::new(());
+}
+
 macro_rules! suite(
     { $s:ident } => {
     #[test]
     fn $s() {
+        let _guard = MUTEX.lock().unwrap();
         assert_eq!(integration_tests::bindings_tests::$s(), 0);
     }
     };