Add middleware tests for __eq__ and test for unique key gen.

tests/core/middleware/test_middleware.py

@@ -0,0 +1,63 @@
+import pytest
+
+from web3 import (
+    Web3,
+)
+from web3.exceptions import (
+    Web3ValueError,
+)
+from web3.middleware import (
+    FormattingMiddlewareBuilder,
+    Web3Middleware,
+)
+
+
+def test_middleware_class_eq_magic_method():
+    w3_a = Web3()
+    w3_b = Web3()
+
+    class TestMiddleware(Web3Middleware):
+        def request_processor(self, method, params):
+            return 1234
+
+    class TestMiddleware2(Web3Middleware):
+        def request_processor(self, method, params):
+            return 4321
+
+    mw1w3_a = TestMiddleware(w3_a)
+    assert mw1w3_a is not None
+    assert mw1w3_a != ""
+
+    mw1w3_a_equal = TestMiddleware(w3_a)
+    assert mw1w3_a == mw1w3_a_equal
+
+    mw2w3_a = TestMiddleware2(w3_a)
+    mw1w3_b = TestMiddleware(w3_b)
+    assert mw1w3_a != mw2w3_a
+    assert mw1w3_a != mw1w3_b
+
+
+def test_unnamed_middleware_are_given_unique_keys(w3):
+    request_formatting_middleware = FormattingMiddlewareBuilder.build(
+        request_formatters={lambda x: x}
+    )
+    request_formatting_middleware2 = FormattingMiddlewareBuilder.build(
+        request_formatters={lambda x: x if x else None}
+    )
+    result_formatting_middleware = FormattingMiddlewareBuilder.build(
+        result_formatters={lambda x: x}
+    )
+    error_formatting_middleware = FormattingMiddlewareBuilder.build(
+        error_formatters={lambda x: x}
+    )
+
+    # adding different middleware should not cause an error
+    w3.middleware_onion.add(request_formatting_middleware)
+    w3.middleware_onion.add(request_formatting_middleware2)
+    w3.middleware_onion.add(result_formatting_middleware)
+    w3.middleware_onion.add(error_formatting_middleware)
+    assert isinstance(w3.eth.block_number, int)
+
+    with pytest.raises(Web3ValueError):
+        # adding the same middleware again should cause an error
+        w3.middleware_onion.add(request_formatting_middleware)