extract assert_exposes unit test.

test/assert_exposes_test.rb

@@ -0,0 +1,38 @@
+require "test_helper"
+
+class AssertExposesTest < Minitest::Spec
+  # TODO: should we test the "meat" of these assertions here?
+  it "#assert_exposes" do
+    test =
+      Class.new(Test) do
+        include Trailblazer::Test::Assertion::AssertExposes
+        Memo = Trailblazer::Test::Testing::Memo
+
+        # 01
+        it do
+          memo = Memo.new(title: "TODO", id: 1)
+
+          assert_exposes memo,
+            id: 1,
+            title: "TODO"
+
+          @result = {}
+        end
+
+        # 02
+        # fails
+        it do
+          memo = Memo.new(title: "TODO", id: 1)
+
+          assert_exposes memo,
+            title: "TODO",
+            content: "this is wrong"
+        end
+      end
+
+    assert_test_case_passes(test, "01", nil)
+    assert_test_case_fails(test, "02", %(#<Minitest::Assertion: Property [content] mismatch.
+Expected: "this is wrong"
+  Actual: nil>))
+  end
+end