Additional checks that the actual value satifies needed method

src/spectator/matchers/contain_matcher.cr

@@ -13,15 +13,21 @@ module Spectator::Matchers
 
     # Checks whether the matcher is satisifed with the expression given to it.
     private def match?(actual : TestExpression(T)) : Bool forall T
+      actual_value = actual.value
+      return unexpected(actual_value, actual.label) unless actual_value.responds_to?(:includes?)
+
       expected.value.all? do |item|
-        actual.value.includes?(item)
+        actual_value.includes?(item)
       end
     end
 
     # If the expectation is negated, then this method is called instead of `#match?`.
     private def does_not_match?(actual : TestExpression(T)) : Bool forall T
+      actual_value = actual.value
+      return unexpected(actual_value, actual.label) unless actual_value.responds_to?(:includes?)
+
       !expected.value.any? do |item|
-        actual.value.includes?(item)
+        actual_value.includes?(item)
       end
     end
 
@@ -54,5 +60,9 @@ module Spectator::Matchers
         superset: actual.value.inspect,
       }
     end
+
+    private def unexpected(value, label)
+      raise "#{label} is not a collection (must respond to `#includes?`). #{label}: #{value.inspect}"
+    end
   end
 end

src/spectator/matchers/empty_matcher.cr

@@ -13,7 +13,10 @@ module Spectator::Matchers
 
     # Checks whether the matcher is satisifed with the expression given to it.
     private def match?(actual : TestExpression(T)) : Bool forall T
-      actual.value.empty?
+      actual_value = actual.value
+      return unexpected(actual_value, actual.label) unless actual_value.responds_to?(:empty?)
+
+      actual_value.empty?
     end
 
     # Message displayed when the matcher isn't satisifed.
@@ -36,5 +39,9 @@ module Spectator::Matchers
     private def failure_message_when_negated(actual) : String
       "#{actual.label} is empty"
     end
+
+    private def unexpected(value, label)
+      raise "#{label} is not a collection (must respond to `#empty?`). #{label}: #{value.inspect}"
+    end
   end
 end

src/spectator/matchers/have_key_matcher.cr

@@ -13,7 +13,10 @@ module Spectator::Matchers
 
     # Checks whether the matcher is satisifed with the expression given to it.
     private def match?(actual : TestExpression(T)) : Bool forall T
-      actual.value.has_key?(expected.value)
+      actual_value = actual.value
+      return unexpected(actual_value, actual.label) unless actual_value.responds_to?(:has_key?)
+
+      actual_value.has_key?(expected.value)
     end
 
     # Message displayed when the matcher isn't satisifed.
@@ -47,5 +50,9 @@ module Spectator::Matchers
         actual: set.inspect,
       }
     end
+
+    private def unexpected(value, label)
+      raise "#{label} is not hash-like (must respond to `#has_key?`). #{label}: #{value.inspect}"
+    end
   end
 end

src/spectator/matchers/have_value_matcher.cr

@@ -13,7 +13,10 @@ module Spectator::Matchers
 
     # Checks whether the matcher is satisifed with the expression given to it.
     private def match?(actual : TestExpression(T)) : Bool forall T
-      actual.value.has_value?(expected.value)
+      actual_value = actual.value
+      return unexpected(actual_value, actual.label) unless actual_value.responds_to?(:has_value?)
+
+      actual_value.has_value?(expected.value)
     end
 
     # Message displayed when the matcher isn't satisifed.
@@ -47,5 +50,9 @@ module Spectator::Matchers
         actual: set.inspect,
       }
     end
+
+    private def unexpected(value, label)
+      raise "#{label} is not hash-like (must respond to `#has_value?`). #{label}: #{value.inspect}"
+    end
   end
 end

src/spectator/matchers/size_matcher.cr

@@ -13,7 +13,10 @@ module Spectator::Matchers
 
     # Checks whether the matcher is satisifed with the expression given to it.
     private def match?(actual : TestExpression(T)) : Bool forall T
-      expected.value == actual.value.size
+      actual_value = actual.value
+      return unexpected(actual_value, actual.label) unless actual_value.responds_to?(:size?)
+
+      expected.value == actual_value.size
     end
 
     # Message displayed when the matcher isn't satisifed.
@@ -54,5 +57,9 @@ module Spectator::Matchers
         actual:   actual.value.size.inspect,
       }
     end
+
+    private def unexpected(value, label)
+      raise "#{label} must respond to `#size`. #{label}: #{value.inspect}"
+    end
   end
 end

src/spectator/matchers/size_of_matcher.cr

@@ -13,7 +13,10 @@ module Spectator::Matchers
 
     # Checks whether the matcher is satisifed with the expression given to it.
     private def match?(actual : TestExpression(T)) : Bool forall T
-      expected.value.size == actual.value.size
+      actual_value = actual.value
+      return unexpected(actual_value, actual.label) unless actual_value.responds_to?(:size?)
+
+      expected.value.size == actual_value.size
     end
 
     # Message displayed when the matcher isn't satisifed.
@@ -54,5 +57,9 @@ module Spectator::Matchers
         actual:   actual.value.size.inspect,
       }
     end
+
+    private def unexpected(value, label)
+      raise "#{label} must respond to `#size`. #{label}: #{value.inspect}"
+    end
   end
 end