tests: add check with prefilling update on block rows (#75162)

tests/form_pages/test_prefill.py

@@ -1717,3 +1717,44 @@ def test_form_page_user_data_source(pub):
         resp = login(get_app(pub), username='foo', password='foo').get('/test/')
         assert resp.form['f1'].value == str(user.id)
         assert 'invalid value selected' not in resp.text
+
+
+def test_form_page_template_block_rows_prefilled_with_form_data(pub):
+    BlockDef.wipe()
+    create_user(pub)
+
+    block = BlockDef()
+    block.name = 'foobar'
+    block.fields = [
+        fields.StringField(
+            id='123',
+            required=True,
+            label='Test',
+            varname='test',
+            prefill={'type': 'string', 'value': '{{ form_var_foo }}'},
+        ),
+    ]
+    block.store()
+
+    formdef = create_formdef()
+    formdef.data_class().wipe()
+    formdef.fields = [
+        fields.PageField(id='1', label='page1'),
+        fields.StringField(id='2', label='text', varname='foo'),
+        fields.PageField(id='3', label='page2'),
+        fields.BlockField(id='4', label='test', block_slug='foobar', max_items=3),
+    ]
+    formdef.store()
+
+    resp = get_app(pub).get('/test/')
+    resp.form['f2'] = 'foo'
+    resp = resp.form.submit('submit')  # -> second page
+    assert resp.form['f4$element0$f123'].value == 'foo'
+    resp = resp.form.submit('f4$add_element')
+    assert resp.form['f4$element1$f123'].value == 'foo'
+    resp.form['f4$element0$f123'] = 'bar'
+    resp = resp.form.submit('previous')  # -> first page
+    resp.form['f2'] = 'baz'
+    resp = resp.form.submit('submit')  # -> second page
+    assert resp.form['f4$element0$f123'].value == 'bar'  # not changed
+    assert resp.form['f4$element1$f123'].value == 'baz'  # updated