From ea954b43389feef6ca0323c95f858df82b17cce6 Mon Sep 17 00:00:00 2001
From: Matthias <xmatthias@outlook.com>
Date: Tue, 2 Jun 2020 20:54:14 +0200
Subject: [PATCH 1/3] Add failing test with testcase from incident

Full problem in #3431
---
 tests/exchange/test_exchange.py | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/tests/exchange/test_exchange.py b/tests/exchange/test_exchange.py
index 25aecba5c..32163f696 100644
--- a/tests/exchange/test_exchange.py
+++ b/tests/exchange/test_exchange.py
@@ -2192,12 +2192,18 @@ def test_extract_cost_curr_rate(mocker, default_conf, order, expected) -> None:
         'fee': {'currency': 'NEO', 'cost': 0.0012}}, 0.001944),
     ({'symbol': 'ETH/BTC', 'amount': 2.21, 'cost': 0.02992561,
         'fee': {'currency': 'NEO', 'cost': 0.00027452}}, 0.00074305),
-    # TODO: More tests here!
     # Rate included in return - return as is
     ({'symbol': 'ETH/BTC', 'amount': 0.04, 'cost': 0.05,
         'fee': {'currency': 'USDT', 'cost': 0.34, 'rate': 0.01}}, 0.01),
     ({'symbol': 'ETH/BTC', 'amount': 0.04, 'cost': 0.05,
         'fee': {'currency': 'USDT', 'cost': 0.34, 'rate': 0.005}}, 0.005),
+    # 0.1% filled - no costs (kraken - #3431)
+    ({'symbol': 'ETH/BTC', 'amount': 0.04, 'cost': 0.0,
+      'fee': {'currency': 'BTC', 'cost': 0.0, 'rate': None}}, None),
+    ({'symbol': 'ETH/BTC', 'amount': 0.04, 'cost': 0.0,
+      'fee': {'currency': 'ETH', 'cost': 0.0, 'rate': None}}, 0.0),
+    ({'symbol': 'ETH/BTC', 'amount': 0.04, 'cost': 0.0,
+      'fee': {'currency': 'NEO', 'cost': 0.0, 'rate': None}}, None),
 ])
 def test_calculate_fee_rate(mocker, default_conf, order, expected) -> None:
     mocker.patch('freqtrade.exchange.Exchange.fetch_ticker', return_value={'last': 0.081})

From a2551daf12c68434449ea512433482cfc2736696 Mon Sep 17 00:00:00 2001
From: Matthias <xmatthias@outlook.com>
Date: Tue, 2 Jun 2020 20:55:12 +0200
Subject: [PATCH 2/3] Fix ZeroDivision problem where cost is 0.0

---
 freqtrade/exchange/exchange.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/freqtrade/exchange/exchange.py b/freqtrade/exchange/exchange.py
index 7ef0d7750..4acee710a 100644
--- a/freqtrade/exchange/exchange.py
+++ b/freqtrade/exchange/exchange.py
@@ -1104,9 +1104,12 @@ class Exchange:
                 order['fee']['cost'] / safe_value_fallback(order, order, 'filled', 'amount'), 8)
         elif fee_curr in self.get_pair_quote_currency(order['symbol']):
             # Quote currency - divide by cost
-            return round(order['fee']['cost'] / order['cost'], 8)
+            return round(order['fee']['cost'] / order['cost'], 8) if order['cost'] else None
         else:
             # If Fee currency is a different currency
+            if not order['cost']:
+                # If cost is None or 0.0 -> falsy, return None
+                return None
             try:
                 comb = self.get_valid_pair_combination(fee_curr, self._config['stake_currency'])
                 tick = self.fetch_ticker(comb)

From ad61673d6feec44a91c48cf805381cca28f11cee Mon Sep 17 00:00:00 2001
From: Matthias <xmatthias@outlook.com>
Date: Tue, 2 Jun 2020 21:10:12 +0200
Subject: [PATCH 3/3] Fix missing key in test order

---
 tests/conftest.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tests/conftest.py b/tests/conftest.py
index 971f7a5fa..1cd3bcc0f 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -1590,6 +1590,7 @@ def buy_order_fee():
         'datetime': str(arrow.utcnow().shift(minutes=-601).datetime),
         'price': 0.245441,
         'amount': 8.0,
+        'cost': 1.963528,
         'remaining': 90.99181073,
         'status': 'closed',
         'fee': None