Pass the section tag in form's hidden field - so it's available for P…

…OST request

app/main/forms.py

@@ -2304,6 +2304,10 @@ def check_url(self, *args, **kwargs):
 
 
 class ChooseDocsForm(StripWhitespaceForm):
+
+    def __init__(self, section_tag):
+        super().__init__(section_tag=section_tag)
+
     docs_version = GovukRadiosField(
         "Which version of the docs would you like to view?",
         choices=[
@@ -2318,6 +2322,7 @@ class ChooseDocsForm(StripWhitespaceForm):
         ],
         thing="a language version of GOV.UK Notify's API docs",
     )
+    section_tag = HiddenField("section tag")
 
 
 class SMSPrefixForm(StripWhitespaceForm):

app/main/views/index.py

@@ -177,7 +177,7 @@ def guidance_api_documentation_section():
 
 @main.route("/using-notify/api-documentation/section/choose-docs")
 def guidance_api_documentation_section_choose_docs():
-    form = ChooseDocsForm()
+    form = ChooseDocsForm(section_tag=request.args.get("section_tag"))
     return render_template(
         "views/guidance/using-notify/api-documentation-section-choose-docs.html",
         navigation_links=using_notify_nav(),

tests/app/main/views/test_index.py

@@ -454,3 +454,8 @@ def test_GET_guidance_api_documentation_section_choose_docs(client_request):
     assert ["python", "ruby", "java", "node", "net", "php", "rest-api", "rest-api"] == [
         radio["value"] for radio in page.select("input[type=radio]")
     ]
+    form = page.select_one("form")
+    assert form["action"] == url_for(
+        "main.guidance_api_documentation_section_choose_docs",
+        section_tag="send-a-file-by-email",
+    )