1 files changed, 46 insertions, 0 deletions
diff --git a/test/unit/tx-state-history-helper.js b/test/unit/tx-state-history-helper.js
new file mode 100644
index 000000000..79ee26d6e
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+++ b/test/unit/tx-state-history-helper.js
@@ -0,0 +1,46 @@
+const assert = require('assert')
+const txStateHistoryHelper = require('../../app/scripts/lib/tx-state-history-helper')
+const testVault = require('../data/v17-long-history.json')
+
+
+describe('tx-state-history-helper', function () {
+  it('migrates history to diffs and can recover original values', function () {
+    testVault.data.TransactionController.transactions.forEach((tx, index) => {
+      const newHistory = txStateHistoryHelper.migrateFromSnapshotsToDiffs(tx.history)
+      newHistory.forEach((newEntry, index) => {
+        if (index === 0) {
+          assert.equal(Array.isArray(newEntry), false, 'initial history item IS NOT a json patch obj')
+        } else {
+          assert.equal(Array.isArray(newEntry), true, 'non-initial history entry IS a json patch obj')
+        }
+        const oldEntry = tx.history[index]
+        const historySubset = newHistory.slice(0, index + 1)
+        const reconstructedValue = txStateHistoryHelper.replayHistory(historySubset)
+        assert.deepEqual(oldEntry, reconstructedValue, 'was able to reconstruct old entry from diffs')
+      })
+    })
+  })
+
+  it('replaying history does not mutate the original obj', function () {
+    const initialState = { test: true, message: 'hello', value: 1 }
+    const diff1 = [{
+      "op": "replace",
+      "path": "/message",
+      "value": "haay",
+    }]
+    const diff2 = [{
+      "op": "replace",
+      "path": "/value",
+      "value": 2,
+    }]
+    const history = [initialState, diff1, diff2]
+
+    const beforeStateSnapshot = JSON.stringify(initialState)
+    const latestState = txStateHistoryHelper.replayHistory(history)
+    const afterStateSnapshot = JSON.stringify(initialState)
+
+    assert.notEqual(initialState, latestState, 'initial state is not the same obj as the latest state')
+    assert.equal(beforeStateSnapshot, afterStateSnapshot, 'initial state is not modified during run')
+  })
+
+})