Fix review comments

docs/configuration.md

@@ -42,6 +42,13 @@ The table below will list all configuration parameters.
 The definition of each config parameters is in 
 [misc.py](https://github.com/gcarq/freqtrade/blob/develop/freqtrade/misc.py#L205).
 
+### Understand stake_amount
+`stake_amount` is an amount of crypto-currency your bot will use for each trade.
+The minimal value is 0.0005. If there is not enough crypto-currency in 
+the account an exception is generated.
+To allow the bot to trade all the avaliable `stake_currency` in your account set `stake_amount` = `unlimited`.
+In this case a trade amount is calclulated as `currency_balanse / (max_open_trades - current_open_trades)`.
+
 ### Understand minimal_roi
 `minimal_roi` is a JSON object where the key is a duration
 in minutes and the value is the minimum ROI in percent.

freqtrade/constants.py

@@ -33,10 +33,11 @@ CONF_SCHEMA = {
         'max_open_trades': {'type': 'integer', 'minimum': 0},
         'ticker_interval': {'type': 'string', 'enum': list(TICKER_INTERVAL_MINUTES.keys())},
         'stake_currency': {'type': 'string', 'enum': ['BTC', 'ETH', 'USDT']},
-        'stake_amount': {'anyOf': [
+        'stake_amount': {
-            {'type': 'integer', 'minimum': 0.0005},
+            "type": ["number", "string"],
-            {'constant': UNLIMITED_STAKE_AMOUNT}
+            "minimum": 0.0005,
-        ]},
+            "pattern": UNLIMITED_STAKE_AMOUNT
+        },
         'fiat_display_currency': {'type': 'string', 'enum': ['AUD', 'BRL', 'CAD', 'CHF',
                                                              'CLP', 'CNY', 'CZK', 'DKK',
                                                              'EUR', 'GBP', 'HKD', 'HUF',

freqtrade/tests/optimize/test_backtesting.py

@@ -3,6 +3,7 @@
 import json
 import math
 import random
+import pytest
 from copy import deepcopy
 from typing import List
 from unittest.mock import MagicMock
@@ -11,7 +12,7 @@ import numpy as np
 import pandas as pd
 from arrow import Arrow
 
-from freqtrade import optimize
+from freqtrade import optimize, constants, DependencyException
 from freqtrade.analyze import Analyze
 from freqtrade.arguments import Arguments
 from freqtrade.optimize.backtesting import Backtesting, start, setup_configuration
@@ -261,6 +262,28 @@ def test_setup_configuration_with_arguments(mocker, default_conf, caplog) -> Non
     )
 
 
+def test_setup_configuration_unlimited_stake_amount(mocker, default_conf, caplog) -> None:
+    """
+    Test setup_configuration() function
+    """
+
+    conf = deepcopy(default_conf)
+    conf['stake_amount'] = constants.UNLIMITED_STAKE_AMOUNT
+
+    mocker.patch('freqtrade.configuration.open', mocker.mock_open(
+        read_data=json.dumps(conf)
+    ))
+
+    args = [
+        '--config', 'config.json',
+        '--strategy', 'DefaultStrategy',
+        'backtesting'
+    ]
+
+    with pytest.raises(DependencyException, match=r'.*stake amount.*'):
+        setup_configuration(get_args(args))
+
+
 def test_start(mocker, fee, default_conf, caplog) -> None:
     """
     Test start() function

freqtrade/tests/test_configuration.py

@@ -53,6 +53,18 @@ def test_load_config_missing_attributes(default_conf) -> None:
         configuration._validate_config(conf)
 
 
+def test_load_config_incorrect_stake_amount(default_conf) -> None:
+    """
+    Test the configuration validator with a missing attribute
+    """
+    conf = deepcopy(default_conf)
+    conf['stake_amount'] = 'fake'
+
+    with pytest.raises(ValidationError, match=r'.*\'fake\' does not match \'unlimited\'.*'):
+        configuration = Configuration([])
+        configuration._validate_config(conf)
+
+
 def test_load_config_file(default_conf, mocker, caplog) -> None:
     """
     Test Configuration._load_config_file() method

freqtrade/tests/test_freqtradebot.py

@@ -295,6 +295,12 @@ def test_get_trade_stake_amount_unlimited_amount(default_conf,
     result = freqtrade._get_trade_stake_amount()
     assert(result == default_conf['stake_amount'] / (conf['max_open_trades'] - 1))
 
+    # create 2 trades, order amount should be 0
+    freqtrade.create_trade()
+
+    result = freqtrade._get_trade_stake_amount()
+    assert(result == 0)
+
 
 def test_create_trade_no_stake_amount(default_conf, ticker, limit_buy_order, fee, mocker) -> None:
     """