test: Add test demonstrating infinite loop.

Author: ludofischer

src/__tests__/integration.js

@@ -0,0 +1,30 @@
+import test from 'ava';
+import postcss from 'postcss';
+
+import reduceCalc from '../../dist';
+
+const testPlugin = {
+  postcssPlugin: 'testplugin',
+  Declaration(decl) {
+    if (decl.value.startsWith('calc')) {
+      decl.value = 'calc(50%-0.5rem)'
+    }
+  }
+}
+
+const processor = postcss([reduceCalc, testPlugin]);
+
+const css = `.item {
+  align-self: flex-end;
+  flex-basis: calc((100% - 1rem) / 2);
+}`;
+
+test('handles a different plugin changing the same declaration', t => {
+  t.plan(1);
+  return processor.process(css, {from: undefined}).then(result => {
+    t.deepEqual(result.css,  `.item {
+  align-self: flex-end;
+  flex-basis: calc(50% - 0.5rem);
+}`);
+  });
+})