Test compiled native extensions on Travis CI

.travis.yml

@@ -1,4 +1,6 @@
 install: git clone https://github.com/sstephenson/bats.git
-script: bats/bin/bats --tap test
-# skips unnecessary Ruby-specific setup
+script: PATH="./bats/bin:$PATH" test/run
 language: c
+env:
+  - RBENV_NATIVE_EXT=
+  - RBENV_NATIVE_EXT=1

test/run

@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+set -e
+
+if [ -n "$RBENV_NATIVE_EXT" ]; then
+  make -C src
+fi
+
+exec bats ${CI:+--tap} test