Add spec for nil matcher

spec/matchers/nil_matcher_spec.cr

@@ -0,0 +1,55 @@
+require "../spec_helper"
+
+describe Spectator::Matchers::NilMatcher do
+  describe "#match?" do
+    context "with nil" do
+      it "is true" do
+        value = nil.as(Bool?)
+        partial = Spectator::Expectations::ValueExpectationPartial.new(value)
+        matcher = Spectator::Matchers::NilMatcher.new
+        matcher.match?(partial).should be_true
+      end
+    end
+
+    context "with not nil" do
+      it "is false" do
+        value = true.as(Bool?)
+        partial = Spectator::Expectations::ValueExpectationPartial.new(value)
+        matcher = Spectator::Matchers::NilMatcher.new
+        matcher.match?(partial).should be_false
+      end
+    end
+  end
+
+  describe "#message" do
+    it "mentions nil" do
+      partial = Spectator::Expectations::ValueExpectationPartial.new(42)
+      matcher = Spectator::Matchers::NilMatcher.new
+      matcher.message(partial).should contain("nil")
+    end
+
+    it "contains the actual label" do
+      value = 42
+      label = "everything"
+      partial = Spectator::Expectations::ValueExpectationPartial.new(label, value)
+      matcher = Spectator::Matchers::NilMatcher.new
+      matcher.message(partial).should contain(label)
+    end
+  end
+
+  describe "#negated_message" do
+    it "mentions nil" do
+      partial = Spectator::Expectations::ValueExpectationPartial.new(42)
+      matcher = Spectator::Matchers::NilMatcher.new
+      matcher.negated_message(partial).should contain("nil")
+    end
+
+    it "contains the actual label" do
+      value = 42
+      label = "everything"
+      partial = Spectator::Expectations::ValueExpectationPartial.new(label, value)
+      matcher = Spectator::Matchers::NilMatcher.new
+      matcher.negated_message(partial).should contain(label)
+    end
+  end
+end