Replace fetch() calls with Turbo form submission via requestSubmit()

setDefaultUnit and drop previously made raw fetch() requests and called
Turbo.renderStreamMessage() manually. Now both create a temporary <form>,
append hidden inputs, and call form.requestSubmit() — Turbo intercepts
the submission natively, handling CSRF, stream responses, and lifecycle.

Also document this convention in CLAUDE.md.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -77,6 +77,28 @@ default/       namespace for default units import/export and admin panel
 root           → /units (authenticated), /sign_in (unauthenticated)
 ```
 
+## JavaScript Conventions
+
+### No manual fetch() — use Turbo
+
+Never make AJAX requests with `fetch()` in JavaScript. Use Turbo's built-in mechanisms instead:
+
+- **Links/buttons that trigger server actions**: use `data: {turbo_stream: true}` on the element (link or button_to form).
+- **Dynamic form submissions from JS** (where HTML alone isn't enough): create a form element, append hidden inputs, and call `form.requestSubmit()`. Turbo intercepts it automatically — no manual CSRF handling, no `Turbo.renderStreamMessage()`.
+  ```javascript
+  var form = document.createElement('form');
+  form.action = url; form.method = 'post'; form.dataset.turboStream = 'true';
+  // append hidden inputs...
+  form.addEventListener('turbo:submit-end', function() { form.remove(); });
+  document.body.appendChild(form);
+  form.requestSubmit();
+  ```
+- **Server-rendered HTML**: use ERB partials and Turbo Stream views (`*.turbo_stream.erb`), never build HTML in JavaScript.
+
+### No HTML generation in JavaScript
+
+Never use JavaScript to build and insert HTML (no `innerHTML =`, no `createElement` trees for content). Render HTML server-side in ERB partials; update the DOM via Turbo Stream actions (`replace`, `update`, `append`, etc.).
+
 ## Database Requirements
 
 The database must support:

app/controllers/measurements_controller.rb

@@ -6,7 +6,7 @@ class MeasurementsController < ApplicationController
   end
 
   def index
-    @measurements = current_user.readouts.includes(:quantity, :unit).order(taken_at: :desc, id: :desc)
+    load_measurements
   end
 
   def new
@@ -20,6 +20,7 @@ class MeasurementsController < ApplicationController
 
     if @readouts.present? && @readouts.all?(&:valid?)
       ActiveRecord::Base.transaction { @readouts.each(&:save!) }
+      load_measurements
       flash.now[:notice] = t('.success', count: @readouts.size)
     else
       errors = @readouts.flat_map { |r| r.errors.full_messages }
@@ -33,6 +34,7 @@ class MeasurementsController < ApplicationController
 
   def update
     if @readout.update(params.require(:readout).permit(:value, :unit_id, :taken_at))
+      load_measurements
       flash.now[:notice] = t('.success')
     else
       @user_units = current_user.units.ordered
@@ -42,6 +44,7 @@ class MeasurementsController < ApplicationController
 
   def destroy
     @readout.destroy!
+    load_measurements
     flash.now[:notice] = t('.success')
   end
 
@@ -50,4 +53,10 @@ class MeasurementsController < ApplicationController
   def find_readout
     @readout = current_user.readouts.find(params[:id])
   end
+
+  def load_measurements
+    @measurements = current_user.readouts.includes(:quantity, :unit).order(taken_at: :desc, id: :desc)
+    @wide_groups = @measurements.group_by(&:taken_at)
+    @wide_quantities = @measurements.map(&:quantity).uniq.sort_by(&:name)
+  end
 end

app/javascript/application.js

@@ -22,100 +22,6 @@ function groupMeasurements() {
     });
 }
 
-function buildWideTable() {
-  var tbody = document.getElementById('measurements');
-  var wideContainer = document.getElementById('measurements-wide');
-  if (!tbody || !wideContainer) return;
-
-  var rows = Array.from(tbody.querySelectorAll('tr[data-taken-at]'));
-
-  if (rows.length === 0) { wideContainer.innerHTML = ''; return; }
-
-  // Unique quantities in alphabetical order
-  var qOrder = [], qSeen = new Set();
-  rows.forEach(function(r) {
-    var id = r.dataset.quantityId;
-    if (id && !qSeen.has(id)) { qSeen.add(id); qOrder.push({id: id, name: r.dataset.quantityName}); }
-  });
-  qOrder.sort(function(a, b) { return a.name.localeCompare(b.name); });
-
-  // Group rows by taken_at, preserving order
-  var groups = [], groupMap = new Map();
-  rows.forEach(function(r) {
-    var key = r.dataset.takenAt || '';
-    if (!groupMap.has(key)) { var g = {rows: []}; groups.push(g); groupMap.set(key, g); }
-    groupMap.get(key).rows.push(r);
-  });
-
-  // Read column headers from compact thead
-  var ths = document.querySelectorAll('.measurements-compact thead th');
-  var takenAtHeader = ths[3] ? ths[3].textContent : '';
-  var createdAtHeader = ths[4] ? ths[4].textContent : '';
-
-  var table = document.createElement('table');
-  table.className = 'items-table';
-
-  // Header
-  var thead = table.createTHead();
-  var hrow = thead.insertRow();
-  [takenAtHeader].concat(qOrder.map(function(q) { return q.name; })).concat([createdAtHeader]).forEach(function(text) {
-    var th = document.createElement('th');
-    th.textContent = text;
-    hrow.appendChild(th);
-  });
-
-  // Body
-  var tbodyEl = table.createTBody();
-  groups.forEach(function(group) {
-    var tr = tbodyEl.insertRow();
-
-    // Taken at
-    var tdTime = tr.insertCell();
-    var takenAtEl = group.rows[0].querySelector('.taken-at');
-    tdTime.textContent = takenAtEl ? takenAtEl.textContent : '';
-
-    // One cell per quantity
-    qOrder.forEach(function(q) {
-      var td = tr.insertCell();
-      var readoutRow = group.rows.find(function(r) { return r.dataset.quantityId === q.id; });
-      if (readoutRow) {
-        td.className = 'ralign';
-        var wrap = document.createElement('span');
-        wrap.className = 'wide-cell';
-        var editLink = readoutRow.querySelector('a.link');
-        if (editLink) {
-          var editUrl = editLink.href + (editLink.href.includes('?') ? '&' : '?') + 'view=wide';
-          var btn = document.createElement('button');
-          btn.className = 'link';
-          btn.type = 'button';
-          btn.dataset.editUrl = editUrl;
-          btn.addEventListener('click', function() { editMeasurementWide(this.dataset.editUrl); this.blur(); });
-          btn.textContent = readoutRow.dataset.value;
-          wrap.appendChild(btn);
-          wrap.appendChild(document.createTextNode('\u00a0' + readoutRow.dataset.unit));
-        } else {
-          wrap.appendChild(document.createTextNode(readoutRow.dataset.value + '\u00a0' + readoutRow.dataset.unit));
-        }
-        var srcActions = readoutRow.querySelector('td.flex');
-        if (srcActions) srcActions.querySelectorAll('form').forEach(function(f) {
-          var cloned = f.cloneNode(true);
-          var span = cloned.querySelector('button span');
-          if (span) span.remove();
-          wrap.appendChild(cloned);
-        });
-        td.appendChild(wrap);
-      }
-    });
-
-    // Created at (from first row of group)
-    var tdCreated = tr.insertCell();
-    var createdAtEl = group.rows[0].querySelector('.created-at');
-    tdCreated.textContent = createdAtEl ? createdAtEl.textContent : '';
-  });
-
-  wideContainer.innerHTML = '';
-  wideContainer.appendChild(table);
-}
 
 function buildCharts() {
   var container = document.getElementById('measurements-charts');
@@ -171,7 +77,6 @@ function getMeasurementsView() {
 
 function applyMeasurementsView(view) {
   document.body.dataset.measurementsView = view;
-  if (view === 'wide') buildWideTable();
 }
 
 function setMeasurementsView(view) {
@@ -191,8 +96,6 @@ document.addEventListener('turbo:load', function() {
   applyMeasurementsView(getMeasurementsView());
   new MutationObserver(function() {
     groupMeasurements();
-    var view = getMeasurementsView();
-    if (view === 'wide') buildWideTable();
   }).observe(tbody, {
     childList: true, subtree: true,
     attributes: true, attributeFilter: ['style']
@@ -227,25 +130,6 @@ window.detailsObserver = new MutationObserver((mutations) => {
   mutations[0].target.dispatchEvent(new Event('change', {bubbles: true}))
 });
 
-function editMeasurementWide(url) {
-  fetch(url, {
-    headers: {
-      'Accept': 'text/vnd.turbo-stream.html',
-      'X-Requested-With': 'XMLHttpRequest'
-    }
-  })
-  .then(response => response.text())
-  .then(html => {
-    Turbo.renderStreamMessage(html);
-    requestAnimationFrame(() => {
-      var panel = document.getElementById('measurement_edit_form');
-      if (panel && panel.firstElementChild) {
-        panel.scrollIntoView({behavior: 'smooth', block: 'nearest'});
-      }
-    });
-  });
-}
-window.editMeasurementWide = editMeasurementWide
 
 function readoutUnitChanged(select) {
   var button = select.closest('tr').querySelector('.set-default-unit');
@@ -263,26 +147,25 @@ window.readoutUnitChanged = readoutUnitChanged
 
 function setDefaultUnit(button) {
   var select = button.closest('tr').querySelector('select[data-default-unit-id]');
-  var params = new URLSearchParams();
+  var form = document.createElement('form');
-  params.append('quantity[default_unit_id]', select.value);
+  form.action = button.dataset.path;
-
+  form.method = 'post';
-  fetch(button.dataset.path, {
+  form.dataset.turboStream = 'true';
-    body: params,
+  var methodInput = document.createElement('input');
-    headers: {
+  methodInput.type = 'hidden'; methodInput.name = '_method'; methodInput.value = 'patch';
-      'Accept': 'text/vnd.turbo-stream.html',
+  var unitInput = document.createElement('input');
-      'X-CSRF-Token': document.head.querySelector('meta[name=csrf-token]').content,
+  unitInput.type = 'hidden'; unitInput.name = 'quantity[default_unit_id]'; unitInput.value = select.value;
-      'X-Requested-With': 'XMLHttpRequest'
+  form.appendChild(methodInput);
-    },
+  form.appendChild(unitInput);
-    method: 'PATCH'
+  form.addEventListener('turbo:submit-end', function(event) {
-  })
+    if (event.detail.success) {
-  .then(response => {
-    if (response.ok) {
       select.dataset.defaultUnitId = select.value;
       readoutUnitChanged(select);
     }
-    return response.text();
+    form.remove();
-  })
+  });
-  .then(html => Turbo.renderStreamMessage(html));
+  document.body.appendChild(form);
+  form.requestSubmit();
 }
 window.setDefaultUnit = setDefaultUnit
 
@@ -455,22 +338,17 @@ window.dragEnd = dragEnd
 
 function drop(event) {
   event.preventDefault()
-
+  var idParam = event.currentTarget.getAttribute("data-drop-id-param")
-  var params = new URLSearchParams()
-  var id_param = event.currentTarget.getAttribute("data-drop-id-param")
   var id = event.currentTarget.getAttribute("data-drop-id").split("_").pop()
-  params.append(id_param, id)
+  var form = document.createElement('form');
-
+  form.action = event.dataTransfer.getData("text/plain");
-  fetch(event.dataTransfer.getData("text/plain"), {
+  form.method = 'post';
-    body: params,
+  form.dataset.turboStream = 'true';
-    headers: {
+  var input = document.createElement('input');
-      "Accept": "text/vnd.turbo-stream.html",
+  input.type = 'hidden'; input.name = idParam; input.value = id;
-      "X-CSRF-Token": document.head.querySelector("meta[name=csrf-token]").content,
+  form.appendChild(input);
-      "X-Requested-With": "XMLHttpRequest"
+  form.addEventListener('turbo:submit-end', function() { form.remove(); });
-    },
+  document.body.appendChild(form);
-    method: "POST"
+  form.requestSubmit();
-  })
-  .then(response => response.text())
-  .then(html => Turbo.renderStreamMessage(html))
 }
 window.drop = drop

app/views/measurements/_wide_table.html.erb

@@ -0,0 +1,41 @@
+<table class="items-table">
+  <thead>
+    <tr>
+      <th><%= Readout.human_attribute_name(:taken_at) %></th>
+      <% wide_quantities.each do |q| %>
+        <th><%= q.name %></th>
+      <% end %>
+      <th><%= Readout.human_attribute_name(:created_at) %></th>
+    </tr>
+  </thead>
+  <tbody>
+    <% wide_groups.each do |taken_at, readouts| %>
+      <tr>
+        <td><%= l(taken_at) if taken_at %></td>
+        <% wide_quantities.each do |q| %>
+          <% readout = readouts.find { |r| r.quantity_id == q.id } %>
+          <td class="ralign">
+            <% if readout %>
+              <span class="wide-cell">
+                <% if current_user.at_least(:active) %>
+                  <%= link_to format("%.10g", readout.value),
+                    edit_measurement_path(readout, view: :wide),
+                    class: 'link', onclick: 'this.blur();',
+                    data: {turbo_stream: true} %>
+                <% else %>
+                  <%= format("%.10g", readout.value) %>
+                <% end %>
+                &nbsp;<%= readout.unit.symbol %>
+                <% if current_user.at_least(:active) %>
+                  <%= image_button_to '', 'delete-outline', measurement_path(readout),
+                    method: :delete, data: {turbo_stream: true} %>
+                <% end %>
+              </span>
+            <% end %>
+          </td>
+        <% end %>
+        <td><%= l(readouts.first.created_at) %></td>
+      </tr>
+    <% end %>
+  </tbody>
+</table>

app/views/measurements/create.turbo_stream.erb

@@ -0,0 +1,13 @@
+<% if @readouts.present? && @readouts.all?(&:persisted?) %>
+  <%= turbo_stream.update :flashes %>
+  <%= turbo_stream.remove :measurement_form %>
+  <%= turbo_stream.enable :new_measurement_link %>
+  <%= turbo_stream.remove :no_items %>
+  <% @readouts.each do |readout| %>
+    <%= turbo_stream.prepend :measurements, partial: 'readout', locals: {readout: readout} %>
+  <% end %>
+  <%= turbo_stream.update 'measurements-wide', partial: 'wide_table',
+    locals: {wide_groups: @wide_groups, wide_quantities: @wide_quantities} %>
+<% else %>
+  <%= turbo_stream.update :flashes %>
+<% end %>

app/views/measurements/destroy.turbo_stream.erb

@@ -0,0 +1,5 @@
+<%= turbo_stream.update :flashes %>
+<%= turbo_stream.remove @readout %>
+<%= turbo_stream.append(:measurements, render_no_items) if current_user.readouts.empty? %>
+<%= turbo_stream.update 'measurements-wide', partial: 'wide_table',
+  locals: {wide_groups: @wide_groups, wide_quantities: @wide_quantities} %>

app/views/measurements/index.html.erb

@@ -22,8 +22,8 @@
         <th><%= Quantity.model_name.human %></th>
         <th><%= Readout.human_attribute_name(:value) %></th>
         <th><%= Unit.model_name.human %></th>
-        <th><%= Readout.human_attribute_name(:taken_at) %></th>
+        <th data-column="taken-at"><%= Readout.human_attribute_name(:taken_at) %></th>
-        <th><%= Readout.human_attribute_name(:created_at) %></th>
+        <th data-column="created-at"><%= Readout.human_attribute_name(:created_at) %></th>
         <% if current_user.at_least(:active) %>
           <th></th>
         <% end %>
@@ -34,7 +34,8 @@
     </tbody>
   </table>
 
-  <div id="measurements-wide" class="measurements-wide"></div>
+  <div id="measurements-wide" class="measurements-wide">
-
+    <%= render 'wide_table', wide_groups: @wide_groups, wide_quantities: @wide_quantities %>
+  </div>
 </div>
 

app/views/measurements/update.turbo_stream.erb

@@ -1,2 +1,4 @@
 <%= turbo_stream.close_form dom_id(@readout, :edit) %>
 <%= turbo_stream.replace @readout, partial: 'measurements/readout', locals: {readout: @readout} %>
+<%= turbo_stream.update 'measurements-wide', partial: 'wide_table',
+  locals: {wide_groups: @wide_groups, wide_quantities: @wide_quantities} %>

db/migrate/20260402000000_add_taken_at_to_readouts.rb

@@ -1,5 +1,6 @@
 class AddTakenAtToReadouts < ActiveRecord::Migration[7.2]
   def change
     add_column :readouts, :taken_at, :datetime
+    add_index :readouts, [:user_id, :taken_at]
   end
 end

db/schema.rb

@@ -39,6 +39,7 @@ ActiveRecord::Schema[7.2].define(version: 2026_04_03_000000) do
     t.index ["quantity_id"], name: "index_readouts_on_quantity_id"
     t.index ["unit_id"], name: "index_readouts_on_unit_id"
     t.index ["user_id"], name: "index_readouts_on_user_id"
+    t.index ["user_id", "taken_at"], name: "index_readouts_on_user_id_and_taken_at"
   end
 
   create_table "units", charset: "utf8mb4", collation: "utf8mb4_0900_as_ci", force: :cascade do |t|

db/seeds.rb

@@ -21,3 +21,4 @@ end
 #[Source, Quantity, Unit].each { |model| model.defaults.delete_all }
 
 require_relative 'seeds/units.rb'
+require_relative 'seeds/demo.rb'

db/seeds/demo.rb

@@ -0,0 +1,87 @@
+demo_email = 'demo@localhost'
+
+User.transaction do
+  break if User.find_by(email: demo_email)
+
+  demo = User.create! email: demo_email, password: 'demo123', status: :active do |user|
+    user.skip_confirmation!
+    print "Creating demo account '#{user.email}' with password '#{user.password}'..."
+  end
+  puts "done."
+
+  # --- Units ---
+  u = {}
+  u[:kg]  = demo.units.create! symbol: 'kg',  description: 'kilogram'
+  u[:g]   = demo.units.create! symbol: 'g',   description: 'gram',       base: u[:kg], multiplier: 1e-3
+  u[:cm]  = demo.units.create! symbol: 'cm',  description: 'centimetre'
+  u[:bpm] = demo.units.create! symbol: 'bpm', description: 'beats per minute'
+  u[:pct] = demo.units.create! symbol: '%',   description: 'percent'
+  u[:h]   = demo.units.create! symbol: 'h',   description: 'hour'
+  u[:min] = demo.units.create! symbol: 'min', description: 'minute',     base: u[:h], multiplier: (1.0/60).round(10)
+  u[:kcal]= demo.units.create! symbol: 'kcal',description: 'kilocalorie'
+  u[:mg]  = demo.units.create! symbol: 'mg',  description: 'milligram',  base: u[:kg], multiplier: 1e-6
+  u[:mmhg]= demo.units.create! symbol: 'mmHg',description: 'millimetre of mercury'
+
+  # --- Quantities ---
+  body      = demo.quantities.create! name: 'Body'
+  weight    = demo.quantities.create! name: 'Weight',        parent: body
+  height    = demo.quantities.create! name: 'Height',        parent: body
+  fat       = demo.quantities.create! name: 'Body fat',      parent: body
+
+  cardio    = demo.quantities.create! name: 'Cardiovascular'
+  hr_rest   = demo.quantities.create! name: 'Resting HR',    parent: cardio
+  hr_peak   = demo.quantities.create! name: 'Peak HR',       parent: cardio
+  bp_sys    = demo.quantities.create! name: 'BP systolic',   parent: cardio
+  bp_dia    = demo.quantities.create! name: 'BP diastolic',  parent: cardio
+
+  activity  = demo.quantities.create! name: 'Activity'
+  sleep_dur = demo.quantities.create! name: 'Sleep',         parent: activity
+  calories  = demo.quantities.create! name: 'Calories out',  parent: activity
+
+  nutrition = demo.quantities.create! name: 'Nutrition'
+  cal_in    = demo.quantities.create! name: 'Calories in',   parent: nutrition
+  caffeine  = demo.quantities.create! name: 'Caffeine',      parent: nutrition
+
+  # --- Readouts (60 days of daily-ish data) ---
+  base_time = 60.days.ago.beginning_of_day
+  rng = Random.new(42)
+
+  weight_val  = 82.4
+  fat_val     = 21.5
+  hr_rest_val = 62.0
+
+  60.times do |i|
+    t = base_time + i.days + rng.rand(3600 * 2)
+
+    weight_val  += rng.rand(-0.3..0.3)
+    fat_val     += rng.rand(-0.15..0.15)
+    hr_rest_val += rng.rand(-1.5..1.5)
+    hr_rest_val  = hr_rest_val.clamp(52, 72)
+
+    demo.readouts.create! quantity: weight,   unit: u[:kg],  value: weight_val.round(1),  created_at: t
+    demo.readouts.create! quantity: fat,      unit: u[:pct], value: fat_val.round(1),     created_at: t
+    demo.readouts.create! quantity: hr_rest,  unit: u[:bpm], value: hr_rest_val.round,    created_at: t
+
+    if i % 2 == 0
+      demo.readouts.create! quantity: bp_sys,  unit: u[:mmhg], value: (115 + rng.rand(-8..8)).round, created_at: t
+      demo.readouts.create! quantity: bp_dia,  unit: u[:mmhg], value: (75  + rng.rand(-5..5)).round,  created_at: t
+    end
+
+    if i % 3 == 0
+      demo.readouts.create! quantity: hr_peak, unit: u[:bpm], value: (155 + rng.rand(-10..10)).round, created_at: t
+    end
+
+    demo.readouts.create! quantity: sleep_dur, unit: u[:h],   value: (6.5 + rng.rand(-1.5..1.5)).round(1), created_at: t
+    demo.readouts.create! quantity: calories,  unit: u[:kcal],value: (2100 + rng.rand(-300..300)).round,    created_at: t
+    demo.readouts.create! quantity: cal_in,    unit: u[:kcal],value: (1900 + rng.rand(-400..400)).round,    created_at: t
+
+    if i % 4 == 0
+      demo.readouts.create! quantity: caffeine, unit: u[:mg], value: (200 + rng.rand(-80..80)).round, created_at: t
+    end
+  end
+
+  # height is stable — record once
+  demo.readouts.create! quantity: height, unit: u[:cm], value: 178.0, created_at: base_time
+
+  puts "  Created #{demo.units.count} units, #{demo.quantities.count} quantities, #{demo.readouts.count} readouts."
+end

test/controllers/measurements_controller_test.rb

@@ -1,7 +1,65 @@
 require "test_helper"
 
 class MeasurementsControllerTest < ActionDispatch::IntegrationTest
-  # test "the truth" do
+  setup do
-  #   assert true
+    host! '127.0.0.1'
-  # end
+    @user = users(:alice)
+    post new_user_session_path, params: { user: { email: @user.email, password: 'alice' } }
+    @quantity = @user.quantities.create!(name: 'Weight')
+    @unit = @user.units.create!(symbol: 'kg')
+  end
+
+  test "index returns ok" do
+    get measurements_path
+    assert_response :success
+  end
+
+  test "index requires authentication" do
+    delete destroy_user_session_path
+    get measurements_path
+    assert_response :redirect
+  end
+
+  test "create records readout with taken_at" do
+    taken_at = 1.day.ago.change(usec: 0)
+    assert_difference -> { @user.readouts.count } do
+      post measurements_path, params: {
+        taken_at: taken_at.iso8601,
+        readouts: [{ quantity_id: @quantity.id, value: '82.5', unit_id: @unit.id }]
+      }, as: :turbo_stream
+    end
+    assert_response :success
+    assert_equal taken_at, @user.readouts.last.taken_at
+  end
+
+  test "create with no readouts selected shows alert" do
+    post measurements_path, params: { taken_at: Time.now.iso8601 }, as: :turbo_stream
+    assert_response :success
+  end
+
+  test "destroy removes readout" do
+    readout = @user.readouts.create!(quantity: @quantity, unit: @unit, value: 82.5, taken_at: 1.day.ago)
+    assert_difference -> { @user.readouts.count }, -1 do
+      delete measurement_path(readout), as: :turbo_stream
+    end
+    assert_response :success
+  end
+
+  test "destroy cannot remove another user's readout" do
+    other_quantity = users(:bob).quantities.create!(name: 'Weight')
+    other_unit = users(:bob).units.create!(symbol: 'kg')
+    readout = users(:bob).readouts.create!(quantity: other_quantity, unit: other_unit, value: 70.0, taken_at: 1.day.ago)
+    assert_no_difference -> { users(:bob).readouts.count } do
+      delete measurement_path(readout), as: :turbo_stream
+    end
+  end
+
+  test "update changes readout value" do
+    readout = @user.readouts.create!(quantity: @quantity, unit: @unit, value: 82.5, taken_at: 1.day.ago)
+    patch measurement_path(readout), params: {
+      readout: { value: '83.0', unit_id: @unit.id, taken_at: readout.taken_at.iso8601 }
+    }, as: :turbo_stream
+    assert_response :success
+    assert_in_delta 83.0, readout.reload.value
+  end
 end