add simple memory fuzzing test

test/mips_test_memory.js

@@ -8,10 +8,13 @@ async function write(mm, root, addr, data) {
       root = l.data
     }
   }
-  console.log("new hash", root)
   return root
 }
 
+function randint(n) {
+  return Math.floor(Math.random() * n)
+}
+
 describe("MIPSMemory contract", function () {
   beforeEach(async function () {
     const MIPSMemory = await ethers.getContractFactory("MIPSMemory")
@@ -22,7 +25,9 @@ describe("MIPSMemory contract", function () {
     let root = "0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421"
 
     root = await write(mm, root, 0, 1)
+    console.log("new hash", root)
     root = await write(mm, root, 4, 2)
+    console.log("new hash", root)
 
     expect(await mm.ReadMemory(root, 0)).to.equal(1)
     expect(await mm.ReadMemory(root, 4)).to.equal(2)
@@ -32,8 +37,11 @@ describe("MIPSMemory contract", function () {
     let root = "0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421"
 
     root = await write(mm, root, 0, 1)
+    console.log("new hash", root)
     root = await write(mm, root, 4, 2)
+    console.log("new hash", root)
     root = await write(mm, root, 0x40, 3)
+    console.log("new hash", root)
 
     expect(await mm.ReadMemory(root, 0)).to.equal(1)
     expect(await mm.ReadMemory(root, 4)).to.equal(2)
@@ -44,11 +52,45 @@ describe("MIPSMemory contract", function () {
     let root = "0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421"
 
     root = await write(mm, root, 0x7fffd00c, 1)
+    console.log("new hash", root)
     root = await write(mm, root, 0x7fffd010, 2)
+    console.log("new hash", root)
     root = await write(mm, root, 0x7fffcffc, 3)
+    console.log("new hash", root)
 
     expect(await mm.ReadMemory(root, 0x7fffd00c)).to.equal(1)
     expect(await mm.ReadMemory(root, 0x7fffd010)).to.equal(2)
     expect(await mm.ReadMemory(root, 0x7fffcffc)).to.equal(3)
   })
+  it("fuzzing should be okay", async function() {
+    await mm.AddTrieNode(new Uint8Array([0x80]))
+    let root = "0x56e81f171bcc55a6ff8345e692c0f86e5b48e01b996cadc001622fb5e363b421"
+    let keys = []
+    let values = []
+
+    for (var i = 0; i < 100; i++) {
+      const choice = Math.random()
+      if (choice < 0.5 || keys.length == 0) {
+        // write new key
+        const key = randint(0x4000)*4
+        const value = randint(0x100000000)
+        root = await write(mm, root, key, value)
+        keys.push(key)
+        values.push(value)
+      } else if (choice > 0.7) {
+        // read old key
+        const idx = randint(keys.length)
+        const key = keys[idx]
+        const value = values[idx]
+        expect(await mm.ReadMemory(root, key)).to.equal(value)
+      } else {
+        // rewrite old key
+        const idx = randint(keys.length)
+        const key = keys[idx]
+        const value = randint(0x100000000)
+        root = await write(mm, root, key, value)
+        values[idx] = value
+      }
+    }
+  })
 })