Add inequality matcher

src/spectator/matchers/be_comparison.cr

@@ -55,8 +55,8 @@ module Spectator::Matchers
     # ```
     # expect(0).to be != 1
     # ```
-    def !=(other : ExpectedType) forall ExpectedType
-      raise NotImplementedError.new("be !=")
+    def !=(expected : ExpectedType) forall ExpectedType
+      InequalityMatcher.new(expected)
     end
   end
 end

src/spectator/matchers/inequality_matcher.cr

@@ -0,0 +1,25 @@
+require "./value_matcher"
+
+module Spectator::Matchers
+  # Matcher that tests whether two values do not equal each other.
+  # The values are compared with the `!=` operator.
+  struct InequalityMatcher(ExpectedType) < ValueMatcher(ExpectedType)
+    # 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 : Expectations::ValueExpectationPartial(ActualType)) : Bool forall ActualType
+      partial.actual != expected
+    end
+
+    # Describes the condition that satisfies the matcher.
+    # This is informational and displayed to the end-user.
+    def message(partial : Expectations::ValueExpectationPartial(ActualType)) : String forall ActualType
+      "Expected #{partial.label} to not equal #{label} (using !=)"
+    end
+
+    # Describes the condition that won't satsify the matcher.
+    # This is informational and displayed to the end-user.
+    def negated_message(partial : Expectations::ValueExpectationPartial(ActualType)) : String forall ActualType
+      "Expected #{partial.label} to equal #{label} (using !=)"
+    end
+  end
+end