Coerce should raise if it fails

lib/literal/enum.rb

@@ -153,10 +153,16 @@ def coerce(value)
 				self[value] || begin
 					const_get(value)
 				rescue NameError
-					nil
+					raise ArgumentError.new(
+						"Can't coerce #{value.inspect} into a #{inspect}."
+					)
 				end
 			else
-				self[value]
+				self[value] || raise(
+					ArgumentError.new(
+						"Can't coerce #{value.inspect} into a #{inspect}."
+					)
+				)
 			end
 		end
 

test/enum.test.rb

@@ -47,8 +47,16 @@ class SymbolTypedEnum < Literal::Enum(Symbol)
 	assert_equal Color.coerce(:Red), Color::Red
 end
 
-test ".coerce with invalid symbol returns nil" do
-	assert_equal Color.coerce(:Invalid), nil
+test ".coerce with invalid symbol raises an ArgumentError" do
+	assert_raises ArgumentError do
+		Color.coerce(:Invalid)
+	end
+end
+
+test ".coerce with invalid value raises an ArgumenError" do
+	assert_raises ArgumentError do
+		Color.coerce("invalid value")
+	end
 end
 
 test ".[] looks up the key by value" do