Add test

tests/important-boolean.test.js

@@ -1,5 +1,6 @@
 import fs from 'fs'
 import path from 'path'
+import * as sharedState from '../src/lib/sharedState'
 
 import { run, css } from './util/run'
 
@@ -63,3 +64,56 @@ test('important boolean', () => {
     expect(result.css).toMatchFormattedCss(expected)
   })
 })
+
+test('important rules are not duplicated when rebuilding', async () => {
+  let config = {
+    important: true,
+    content: [path.resolve(__dirname, './important-boolean-duplicates.test.html')],
+  }
+
+  await fs.promises.writeFile(config.content[0], `<div class="mt-2 pt-4"></div>`)
+
+  let input = css`
+    @tailwind utilities;
+  `
+
+  let result = await run(input, config)
+  let allContexts = Array.from(sharedState.contextMap.values())
+
+  let context = allContexts[allContexts.length - 1]
+
+  let ruleCacheSize1 = context.ruleCache.size
+
+  expect(result.css).toMatchFormattedCss(css`
+    .mt-2 {
+      margin-top: 0.5rem !important;
+    }
+    .pt-4 {
+      padding-top: 1rem !important;
+    }
+  `)
+
+  await new Promise((resolve) => setTimeout(resolve, 1000))
+  await fs.promises.writeFile(config.content[0], `<div class="mt-2 pt-6"></div>`)
+
+  result = await run(input, config)
+
+  let ruleCacheSize2 = context.ruleCache.size
+
+  expect(result.css).toMatchFormattedCss(css`
+    .mt-2 {
+      margin-top: 0.5rem !important;
+    }
+    .pt-4 {
+      padding-top: 1rem !important;
+    }
+    .pt-6 {
+      padding-top: 1.5rem !important;
+    }
+  `)
+
+  // The rule cache was effectively doubling in size previously
+  // because the rule cache was never de-duped
+  // This ensures this behavior doesn't return
+  expect(ruleCacheSize2 - ruleCacheSize1).toBeLessThan(10)
+})