restructure testing infrastructure to be more modular

test/core/fixtures/bin/babel-node/require/in-files/bar2.js

@@ -0,0 +1,2 @@
+var bar = () => console.log("bar");
+bar();

test/core/fixtures/bin/babel-node/require/in-files/foo2.js

@@ -0,0 +1,4 @@
+var foo = () => console.log("foo");
+foo();
+
+import "./bar2";

test/core/fixtures/bin/babel-node/require/options.json

@@ -0,0 +1,3 @@
+{
+  "args": ["foo2"]
+}

test/core/fixtures/bin/babel-node/require/stdout.txt

@@ -0,0 +1,2 @@
+foo
+bar