Added Quantity tests

specutils/tests/test_arithmetic.py

@@ -86,9 +86,38 @@ def test_math_with_plain_number(self):
             self.spec * np.ones(self.spec.flux.shape)
 
     def test_math_with_quantity(self):
-        # TODO: Like plain number, but also see Jy * Jy becomes Jy**2, Jy + nJy
-        # TODO: Array Quantity now errors
-        pass
+        q = 1 * u.uJy  # 1000 nJy
+
+        spec_added_fwd = self.spec + q
+        assert_quantity_allclose(spec_added_fwd.flux, 1001 * u.nJy)
+
+        # Quantity has its own __add__
+        with pytest.raises(ValueError, match='Value not scalar compatible'):
+            q + self.spec
+
+        spec_subbed_fwd = self.spec - q
+        assert_quantity_allclose(spec_subbed_fwd.flux, -999 * u.nJy)
+
+        # Quantity has its own __sub__
+        with pytest.raises(ValueError, match='Value not scalar compatible'):
+            q - self.spec
+
+        spec_mul_fwd = self.spec * q
+        assert_quantity_allclose(spec_mul_fwd.flux, 1000 * (u.nJy * u.nJy))
+
+        # Quantity has its own __mul__
+        spec_mul_bak = q * self.spec
+        assert isinstance(spec_mul_bak, u.Quantity)  # Becomes Quantity
+
+        spec_div = self.spec / q
+        assert_quantity_allclose(spec_div.flux, 0.001)
+
+        # Quantity has its own __truediv__
+        with pytest.raises(TypeError, match='unsupported operand'):
+            q / self.spec
+
+        with pytest.raises(ValueError, match='Quantity must be scalar'):
+            self.spec * (self.spec.flux)
 
     def test_math_with_ndcube(self):
         from astropy.wcs import WCS