add balance transfer tests

Add tests to show the error types of different impossible balance transfers.

Since it's only tests describing the current behavior, I merge this without review. We can change the behavior in an other MR.

closes #135 (closed)

runtime/gdev/tests/integration_tests.rs

@@ -184,6 +184,60 @@ fn test_total_issuance_vs_monetary_mass() {
         });
 }
 
+/// test balance transfer
+#[test]
+fn test_simple_transfer() {
+    ExtBuilder::new(1, 3, 4)
+        .with_initial_balances(vec![(AccountKeyring::Alice.to_account_id(), 600)])
+        .build()
+        .execute_with(|| {
+            run_to_block(1);
+            assert_ok!(Balances::transfer_allow_death(
+                frame_system::RawOrigin::Signed(AccountKeyring::Alice.to_account_id()).into(),
+                AccountKeyring::Dave.to_account_id().into(),
+                500
+            ));
+        })
+}
+
+/// test balance transfer without enough balance (would prefer TokenError::BelowMinimum or NotExpendable)
+#[test]
+fn test_simple_transfer_not_enough() {
+    ExtBuilder::new(1, 3, 4)
+        .with_initial_balances(vec![(AccountKeyring::Alice.to_account_id(), 599)])
+        .build()
+        .execute_with(|| {
+            run_to_block(1);
+            assert_noop!(
+                Balances::transfer_allow_death(
+                    frame_system::RawOrigin::Signed(AccountKeyring::Alice.to_account_id()).into(),
+                    AccountKeyring::Dave.to_account_id().into(),
+                    500
+                ),
+                sp_runtime::TokenError::Frozen
+            );
+        })
+}
+
+/// test balance transfer without enough balance (would prefer TokenError::FundsUnavailable)
+#[test]
+fn test_simple_transfer_underflow() {
+    ExtBuilder::new(1, 3, 4)
+        .with_initial_balances(vec![(AccountKeyring::Alice.to_account_id(), 499)])
+        .build()
+        .execute_with(|| {
+            run_to_block(1);
+            assert_noop!(
+                Balances::transfer_allow_death(
+                    frame_system::RawOrigin::Signed(AccountKeyring::Alice.to_account_id()).into(),
+                    AccountKeyring::Dave.to_account_id().into(),
+                    500
+                ),
+                sp_runtime::ArithmeticError::Underflow
+            );
+        })
+}
+
 /// test identity go below ED
 #[test]
 fn test_identity_below_ed() {