Rework test to check for failure to return a spending key

src/gtest/test_keystore.cpp

@@ -5,19 +5,22 @@
 
 TEST(keystore_tests, store_and_retrieve_spending_key) {
     CBasicKeyStore keyStore;
+    libzcash::SpendingKey skOut;
 
     std::set<libzcash::PaymentAddress> addrs;
     keyStore.GetPaymentAddresses(addrs);
     ASSERT_EQ(0, addrs.size());
 
     auto sk = libzcash::SpendingKey::random();
-    keyStore.AddSpendingKey(sk);
-
     auto addr = sk.address();
-    ASSERT_TRUE(keyStore.HaveSpendingKey(addr));
 
-    libzcash::SpendingKey skOut;
-    keyStore.GetSpendingKey(addr, skOut);
+    // Sanity-check: we can't get a key we haven't added
+    ASSERT_FALSE(keyStore.HaveSpendingKey(addr));
+    ASSERT_FALSE(keyStore.GetSpendingKey(addr, skOut));
+
+    keyStore.AddSpendingKey(sk);
+    ASSERT_TRUE(keyStore.HaveSpendingKey(addr));
+    ASSERT_TRUE(keyStore.GetSpendingKey(addr, skOut));
     ASSERT_EQ(sk, skOut);
 
     keyStore.GetPaymentAddresses(addrs);