Allow creation of doubles without a definition

Utilizes anonymous doubles to implement this.
Fixes https://github.com/icy-arctic-fox/spectator/issues/30

CHANGELOG.md

@@ -7,6 +7,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 ### Added
 - Added support for `with(no_args)` for method stubs. [#28](https://github.com/icy-arctic-fox/spectator/issues/28)
+- Allow creation of doubles without definition block. [#30](https://github.com/icy-arctic-fox/spectator/issues/30)
 
 ## [0.9.38] - 2021-05-27
 ### Fixed

spec/issues/github_issue_30_spec.cr

@@ -0,0 +1,9 @@
+require "../spec_helper"
+
+Spectator.describe "GitHub Issue #30" do
+  let(dbl) { double(:foo) }
+
+  it "supports block-less symbol doubles" do
+    expect(dbl).to_not be_nil
+  end
+end

src/spectator/dsl/mocks.cr

@@ -19,13 +19,17 @@ module Spectator::DSL
   end
 
   macro create_double(type_name, name, **stubs)
-    {% type_name.resolve? || raise("Could not find a double labeled #{name}") %}
-
+    {% if type_name.resolve? %}
       {{type_name}}.new.tap do |%double|
         {% for name, value in stubs %}
         allow(%double).to receive({{name.id}}).and_return({{value}})
         {% end %}
       end
+    {% elsif @def %}
+      anonymous_double({{name ? name.stringify : "Anonymous"}}, {{stubs.double_splat}})
+    {% else %}
+      {% raise "Block required for double definition" %}
+    {% end %}
   end
 
   macro define_double(type_name, name, **stubs, &block)
@@ -73,13 +77,17 @@ module Spectator::DSL
   end
 
   macro create_null_double(type_name, name, **stubs)
-    {% type_name.resolve? || raise("Could not find a double labeled #{name}") %}
-
+    {% if type_name.resolve? %}
       {{type_name}}.new(true).tap do |%double|
         {% for name, value in stubs %}
         allow(%double).to receive({{name.id}}).and_return({{value}})
         {% end %}
       end
+    {% elsif @def %}
+      anonymous_null_double({{name ? name.stringify : "Anonymous"}}, {{stubs.double_splat}})
+    {% else %}
+      {% raise "Block required for double definition" %}
+    {% end %}
   end
 
   macro define_null_double(type_name, name, **stubs, &block)