Added depth cache tests

tests/test_depth_cache.py

@@ -0,0 +1,42 @@
+from binance.depthcache import DepthCache
+import pytest
+
+TEST_SYMBOL = "BNBBTC"
+
+
+@pytest.fixture
+def fresh_cache():
+    return DepthCache(TEST_SYMBOL)
+
+
+def test_add_bids(fresh_cache):
+    """Verify basic functionality for adding a bid to the cache"""
+    high_bid = [0.111, 489]
+    mid_bid = [0.018, 300]
+    low_bid = [0.001, 100]
+    for bid in [high_bid, low_bid, mid_bid]:
+        fresh_cache.add_bid(bid)
+
+    bids = fresh_cache.get_bids()
+
+    assert len(bids) == 3
+
+    assert bids == sorted(bids, reverse=True)
+
+
+def test_add_asks(fresh_cache):
+    """Verify basic functionality for adding an ask to the cache"""
+    high_ask = [0.111, 489]
+    mid_ask = [0.018, 300]
+    low_ask = [0.001, 100]
+
+    for ask in [high_ask, low_ask, mid_ask]:
+        fresh_cache.add_ask(ask)
+
+    asks = fresh_cache.get_asks()
+
+    # Three asks should be in the cache
+    assert len(asks) == 3
+
+    # Lowest ask price should be first (ascending order)
+    assert asks == sorted(asks)