new file mode 100644
--- /dev/null
+++ b/dom/media/gtest/TestRust.cpp
@@ -0,0 +1,8 @@
+#include <stdint.h>
+
+extern "C" uint8_t* test_rust();
+
+TEST(rust, CallFromCpp) {
+  auto greeting = test_rust();
+  EXPECT_STREQ(reinterpret_cast<char*>(greeting), "hello from rust.");
+}

new file mode 100644
--- /dev/null
+++ b/dom/media/gtest/hello.rs
@@ -0,0 +1,6 @@
+#[no_mangle]
+pub extern fn test_rust() -> *const u8 {
+    // NB: rust &str aren't null terminated.
+    let greeting = "hello from rust.\0";
+    greeting.as_ptr()
+}

--- a/dom/media/gtest/moz.build
+++ b/dom/media/gtest/moz.build
@@ -24,16 +24,21 @@ if CONFIG['MOZ_EME']:
 
 if CONFIG['MOZ_WEBM_ENCODER']:
     UNIFIED_SOURCES += [
         'TestVideoTrackEncoder.cpp',
         'TestVorbisTrackEncoder.cpp',
         'TestWebMWriter.cpp',
     ]
 
+if CONFIG['MOZ_RUST']:
+    SOURCES += ['hello.rs',]
+    UNIFIED_SOURCES += ['TestRust.cpp',]
+
+
 TEST_HARNESS_FILES.gtest += [
     '../test/gizmo-frag.mp4',
     '../test/gizmo.mp4',
     'dash_dashinit.mp4',
     'mediasource_test.mp4',
     'test.webm',
 ]