refactor: define DepositPreauth transaction model (#1545)

- Defines a TypeScript type for DepositPreauth
- Provides an optional function to users for verifying a DepositPreauth instance at runtime: verifyDepositPreauth()
- Adds tests for verifyDepositPreauth()

test/models/depositPreauth.ts

@@ -0,0 +1,83 @@
+import { ValidationError } from 'xrpl-local/common/errors'
+import { verifyDepositPreauth } from './../../src/models/transactions/depositPreauth'
+import { assert } from 'chai'
+
+/**
+ * DepositPreauth Transaction Verification Testing
+ *
+ * Providing runtime verification testing for each specific transaction type
+ */
+describe('DepositPreauth Transaction Verification', () => {
+    let depositPreauth
+
+    beforeEach(() => {
+        depositPreauth = {
+            TransactionType: 'DepositPreauth',
+            Account: 'rUn84CUYbNjRoTQ6mSW7BVJPSVJNLb1QLo',
+        } as any
+    })
+
+    it ('verifies valid DepositPreauth when only Authorize is provided', () => {
+        depositPreauth.Authorize = 'rsA2LpzuawewSBQXkiju3YQTMzW13pAAdW'
+        assert.doesNotThrow(() => verifyDepositPreauth(depositPreauth))
+    })
+
+    it ('verifies valid DepositPreauth when only Unauthorize is provided', () => {
+        depositPreauth.Unauthorize = 'raKEEVSGnKSD9Zyvxu4z6Pqpm4ABH8FS6n'
+        assert.doesNotThrow(() => verifyDepositPreauth(depositPreauth))
+    })
+
+    it ('throws when both Authorize and Unauthorize are provided', () => {
+        depositPreauth.Authorize = 'rsA2LpzuawewSBQXkiju3YQTMzW13pAAdW'
+        depositPreauth.Unauthorize = 'raKEEVSGnKSD9Zyvxu4z6Pqpm4ABH8FS6n'
+        assert.throws(
+            () => verifyDepositPreauth(depositPreauth),
+            ValidationError,
+            "DepositPreauth: can't provide both Authorize and Unauthorize fields"
+        )
+    })
+
+    it ('throws when neither Authorize nor Unauthorize are provided', () => {
+        assert.throws(
+            () => verifyDepositPreauth(depositPreauth),
+            ValidationError,
+            'DepositPreauth: must provide either Authorize or Unauthorize field'
+        )
+    })
+
+    it ('throws when Authorize is not a string', () => {
+        depositPreauth.Authorize = 1234
+        assert.throws(
+            () => verifyDepositPreauth(depositPreauth),
+            ValidationError,
+            'DepositPreauth: Authorize must be a string'
+        )
+    })
+
+    it ('throws when an Account attempts to preauthorize its own address', () => {
+        depositPreauth.Authorize = depositPreauth.Account
+        assert.throws(
+            () => verifyDepositPreauth(depositPreauth),
+            ValidationError,
+            "DepositPreauth: Account can't preauthorize its own address"
+        )
+    })
+
+    it ('throws when Unauthorize is not a string', () => {
+        depositPreauth.Unauthorize = 1234
+        assert.throws(
+            () => verifyDepositPreauth(depositPreauth),
+            ValidationError,
+            'DepositPreauth: Unauthorize must be a string'
+        )
+    })
+
+    it ('throws when an Account attempts to unauthorize its own address', () => {
+        depositPreauth.Unauthorize = depositPreauth.Account
+        assert.throws(
+            () => verifyDepositPreauth(depositPreauth),
+            ValidationError,
+            "DepositPreauth: Account can't unauthorize its own address"
+        )
+    })
+})