Build fake for numpy array that raises ValueError

Author: jamescooke

tests/fakes.py

@@ -0,0 +1,15 @@
+class FakeNumpyArray():
+
+    def __init__(self, *args, **kwargs):
+        pass
+
+    def __add__(self, other):
+        return self
+
+    def __lt__(self, other):
+        raise ValueError(
+            'Fake for: The truth value of any array with more than one element is ambiguous.'
+        )
+
+    def __abs__(self):
+        return self

tests/test_fake_numpy_array.py

@@ -0,0 +1,52 @@
+import pytest
+
+from fakes import FakeNumpyArray
+
+
+def test():
+    """
+    FakeNumpyArray can be used to trigger a ValueError
+    """
+    left = FakeNumpyArray([1, 2, 3])
+    right = 1
+
+    with pytest.raises(ValueError):
+        abs(left + right) < 19999
+
+
+def test_init():
+    """
+    FakeNumpyArray can init with a list.
+    """
+    result = FakeNumpyArray([1, 2, 3])
+
+    assert isinstance(result, FakeNumpyArray)
+
+
+def test_add():
+    """
+    FakeNumpyArray returns instance of itself when `+ 1` is applied to it.
+    """
+    fake = FakeNumpyArray()
+
+    result = fake + 1
+
+    assert isinstance(result, FakeNumpyArray)
+
+
+def test_abs():
+    fake = FakeNumpyArray()
+
+    result = abs(fake)
+
+    assert isinstance(result, FakeNumpyArray)
+
+
+def test_bool():
+    """
+    Attempting to use a FakeNumpyArray in a boolean expression raises.
+    """
+    fake = FakeNumpyArray()
+
+    with pytest.raises(ValueError):
+        fake < 19999