From 46b75563a0dec4c07d7e622c1e919cdccfa37e6f Mon Sep 17 00:00:00 2001
From: Facundo Medica <14063057+facundomedica@users.noreply.github.com>
Date: Wed, 26 Jul 2023 13:05:04 +0200
Subject: [PATCH] test: Add DiffCollectionsMigration (#17128)

---
 testutil/collections.go | 75 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)
 create mode 100644 testutil/collections.go

diff --git a/testutil/collections.go b/testutil/collections.go
new file mode 100644
index 0000000000..2354943de7
--- /dev/null
+++ b/testutil/collections.go
@@ -0,0 +1,75 @@
+package testutil
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+
+	storetypes "cosmossdk.io/store/types"
+
+	sdk "github.com/cosmos/cosmos-sdk/types"
+)
+
+// DiffCollectionsMigration is meant to aid in the migration from the previous store
+// solution to collections. It takes a few steps to use it:
+//  1. Write a test function that writes elements using the old store solution.
+//  2. Run the test function and copy the hash that it outputs (run it a couple
+//     of times to make sure no non-deterministic data is being used).
+//  3. Change the code to use collections and run the test function again to make
+//     sure the hash didn't change.
+//
+// First we write it as such:
+//
+//	func TestMigrateStore(t *testing.T) {
+//		DiffCollectionsMigration(
+//			ctx,
+//			storeKey,
+//			100,
+//			func(i int64) {
+//				err := SetPreviousProposerConsAddr(ctx, addrs[i])
+//				require.NoError(t, err)
+//			},
+//			"abcdef0123456789",
+//		)
+//	}
+//
+// Then after we change the code to use collections, we modify the writeElem function:
+//
+//	func TestMigrateStore(t *testing.T) {
+//		DiffCollectionsMigration(
+//			ctx,
+//			storeKey,
+//			100,
+//			func(i int64) {
+//				err := keeper.PreviousProposer.Set(ctx, addrs[i])
+//				require.NoError(t, err)
+//			},
+//			"abcdef0123456789",
+//		)
+//	}
+func DiffCollectionsMigration(
+	ctx sdk.Context,
+	storeKey *storetypes.KVStoreKey,
+	iterations int,
+	writeElem func(int64),
+	targetHash string,
+) error {
+	for i := int64(0); i < int64(iterations); i++ {
+		writeElem(i)
+	}
+
+	h := sha256.New()
+	it := ctx.KVStore(storeKey).Iterator(nil, nil)
+	defer it.Close()
+	for ; it.Valid(); it.Next() {
+		h.Write(it.Key())
+		h.Write(it.Value())
+	}
+
+	hash := sha256.Sum256(nil)
+	if hex.EncodeToString(hash[:]) != targetHash {
+		return fmt.Errorf("hashes don't match: %s != %s", hex.EncodeToString(hash[:]), targetHash)
+	}
+
+	return nil
+}