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+# Deno runtime tests
+
+Files in this directory are unit tests for Deno runtime.
+
+Testing Deno runtime code requires checking API under different runtime
+permissions. To accomplish this all tests exercised are created using
+`Deno.test()` function.
+
+```ts
+import {} from "./test_util.ts";
+
+Deno.test(function simpleTestFn(): void {
+  // test code here
+});
+
+Deno.test(
+  {
+    ignore: Deno.build.os === "windows",
+    permissions: { read: true, write: true },
+  },
+  function complexTestFn(): void {
+    // test code here
+  },
+);
+```
+
+## Running tests
+
+There are two ways to run `unit_test_runner.ts`:
+
+```sh
+# Run all tests.
+cargo run --bin deno -- test --allow-all --unstable --location=http://js-unit-tests/foo/bar cli/tests/unit/
+
+# Run a specific test module
+cargo run --bin deno -- test --allow-all --unstable --location=http://js-unit-tests/foo/bar cli/tests/unit/files_test.ts
+```
+
+### Http server
+
+`target/debug/test_server` is required to run when one's running unit tests.
+During CI it's spawned automatically, but if you want to run tests manually make
+sure that server is spawned otherwise there'll be cascade of test failures.