tx state history - fix bug where initial snapshot was mutated on updateTx

app/scripts/lib/tx-state-history-helper.js

@@ -24,7 +24,8 @@ function generateHistoryEntry(previousState, newState) {
   return jsonDiffer.compare(previousState, newState)
 }
 
-function replayHistory(shortHistory) {
+function replayHistory(_shortHistory) {
+  const shortHistory = clone(_shortHistory)
   return shortHistory.reduce((val, entry) => jsonDiffer.applyPatch(val, entry).newDocument)
 }
 

test/unit/tx-state-history-helper.js

@@ -20,4 +20,26 @@ describe('tx-state-history-helper', function () {
       })
     })
   })
+
+  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')
+  })
 })