feat: add more specs

spec/railtie/mailer_spec.rb

@@ -36,6 +36,22 @@ def html_only(to, subject)
     end
   end
 
+  def with_headers_method(to, subject)
+    headers["X-Entity-Ref-ID"] = "123"
+    mail(to: to, subject: subject) do |format|
+      format.text { render plain: "txt" }
+      format.html { render html: "<p>html</p>".html_safe }
+    end
+  end
+
+  def with_overwritten_headers(to, subject)
+    headers["X-Entity-Ref-ID"] = "123"
+    mail(to: to, subject: subject, headers: {"X-Entity-Ref-ID": "overwritten"}) do |format|
+      format.text { render plain: "txt" }
+      format.html { render html: "<p>html</p>".html_safe }
+    end
+  end
+
   def with_attachment(to, subject)
     attachments['invoice.pdf'] = {
       :content => File.read('resources/invoice.pdf'),
@@ -64,7 +80,7 @@ class TestMailerWithDisplayName < TestMailer
     expect(body[:to]).to eql(["[email protected]"])
     expect(body[:html]).to eql("<p>HTML!</p>")
     expect(body[:text]).to eql("text")
-    expect(body[:headers][:"X-Entity-Ref-ID"]).to eql("123")
+    expect(body[:headers]["X-Entity-Ref-ID"]).to eql("123")
   end
 
   it "properly creates a html only msg" do
@@ -106,5 +122,27 @@ class TestMailerWithDisplayName < TestMailer
     expect(body[:to]).to eql(["[email protected]"])
     expect(body[:html]).to be nil
     expect(body[:text]).to eql("text")
+    expect(body[:headers]).to be nil
+  end
+
+  it "properly creates header through headers method" do
+    message = TestMailer.with_headers_method("[email protected]", "Test!")
+    body = @mailer.build_resend_params(message)
+    expect(body[:from]).to eql("[email protected]")
+    expect(body[:to]).to eql(["[email protected]"])
+    expect(body[:html]).to eql("<p>html</p>")
+    expect(body[:text]).to eql("txt")
+    expect(body[:headers]["X-Entity-Ref-ID"]).to eql("123")
+  end
+
+  it "#mail properly overwrites #headers" do
+    message = TestMailer.with_overwritten_headers("[email protected]", "Test!")
+    body = @mailer.build_resend_params(message)
+    expect(body[:from]).to eql("[email protected]")
+    expect(body[:tags]).to eql(nil)
+    expect(body[:to]).to eql(["[email protected]"])
+    expect(body[:html]).to eql("<p>html</p>")
+    expect(body[:text]).to eql("txt")
+    expect(body[:headers]["X-Entity-Ref-ID"]).to eql("overwritten")
   end
 end