Base PredicateMatcher off of Matcher

No need to store an expected value.
Matcher's initializer must be public.

src/spectator/dsl/matcher_dsl.cr

@@ -423,7 +423,7 @@ module Spectator::DSL
     macro method_missing(call)
       {% if call.name.starts_with?("be_") %}
       {% method_name = call.name[3..-1] %} # Remove `be_` prefix.
-      ::Spectator::Matchers::PredicateMatcher.new({{method_name.stringify}}, { {{method_name}}: nil })
+      ::Spectator::Matchers::PredicateMatcher(NamedTuple({{method_name}}: Nil)).new({{method_name.stringify}})
       {% else %}
       {% raise "Undefined local variable or method '#{call}'" %}
       {% end %}

src/spectator/matchers/matcher.cr

@@ -9,7 +9,7 @@ module Spectator::Matchers
     private getter label : String
 
     # Creates the base of the matcher.
-    private def initialize(@label)
+    def initialize(@label)
     end
 
     # Determines whether the matcher is satisfied with the value given to it.

src/spectator/matchers/predicate_matcher.cr

@@ -4,7 +4,7 @@ module Spectator::Matchers
   # Matcher that tests one or more predicates (methods ending in `?`).
   # The `ExpectedType` type param should be a `NamedTuple`.
   # Each key in the tuple is a predicate (without the `?`) to test.
-  struct PredicateMatcher(ExpectedType) < ValueMatcher(ExpectedType)
+  struct PredicateMatcher(ExpectedType) < Matcher
     # Determines whether the matcher is satisfied with the value given to it.
     # True is returned if the match was successful, false otherwise.
     def match?(partial)