From 9ebb2324f2afbe06c08cac1b248530efa5b4fcdc Mon Sep 17 00:00:00 2001
From: Simon Lydell <simon.lydell@gmail.com>
Date: Sat, 12 Jul 2025 09:38:56 +0200
Subject: [PATCH 1/2] Support classes set using the class attribute

---
 src/Test/Html/Internal/ElmHtml/Query.elm | 15 +++++++++++++--
 tests/src/Test/Html/QueryTests.elm       | 19 +++++++++++++++++++
 2 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/src/Test/Html/Internal/ElmHtml/Query.elm b/src/Test/Html/Internal/ElmHtml/Query.elm
index 64b1c36c..95699e60 100644
--- a/src/Test/Html/Internal/ElmHtml/Query.elm
+++ b/src/Test/Html/Internal/ElmHtml/Query.elm
@@ -262,8 +262,19 @@ hasStyle style facts =
 
 classnames : Facts msg -> List String
 classnames facts =
-    Dict.get "className" facts.stringAttributes
-        |> Maybe.withDefault ""
+    (case ( Dict.get "class" facts.stringAttributes, Dict.get "className" facts.stringAttributes ) of
+        ( Just class, Just className ) ->
+            class ++ " " ++ className
+
+        ( Just class, Nothing ) ->
+            class
+
+        ( Nothing, Just className ) ->
+            className
+
+        ( Nothing, Nothing ) ->
+            ""
+    )
         |> String.split " "
 
 
diff --git a/tests/src/Test/Html/QueryTests.elm b/tests/src/Test/Html/QueryTests.elm
index 134ff5c2..3f8141dd 100644
--- a/tests/src/Test/Html/QueryTests.elm
+++ b/tests/src/Test/Html/QueryTests.elm
@@ -113,6 +113,25 @@ all =
                                 [ Query.has [ attribute (Attr.property "className" (Encode.string "hello world")) ]
                                 , Query.has [ attribute (Attr.property "className" (Encode.string "world hello")) ]
                                 ]
+                , test "matches a class added using Attr.attribute" <|
+                    \() ->
+                        divWithAttribute (Attr.attribute "class" "hello")
+                            |> Query.fromHtml
+                            |> Query.has [ class "hello" ]
+                , test "matches a class added using Attr.property" <|
+                    \() ->
+                        divWithAttribute (Attr.property "className" (Encode.string "hello"))
+                            |> Query.fromHtml
+                            |> Query.has [ class "hello" ]
+                , test "matches one class added using Attr.attribute and one added using Attr.property" <|
+                    \() ->
+                        Html.div
+                            [ Attr.attribute "class" "hello"
+                            , Attr.property "className" (Encode.string "world")
+                            ]
+                            []
+                            |> Query.fromHtml
+                            |> Query.has [ class "hello", class "world" ]
                 ]
             ]
         , describe "Query.contains" <|

From 0238246dd68a34970b1df4cb461c5c94c62eba25 Mon Sep 17 00:00:00 2001
From: Simon Lydell <simon.lydell@gmail.com>
Date: Sat, 12 Jul 2025 19:25:06 +0200
Subject: [PATCH 2/2] Match nothing if both class and className are used

---
 src/Test/Html/Internal/ElmHtml/Query.elm | 10 ++++++++--
 tests/src/Test/Html/QueryTests.elm       |  6 ++++--
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/Test/Html/Internal/ElmHtml/Query.elm b/src/Test/Html/Internal/ElmHtml/Query.elm
index 95699e60..8482e5ec 100644
--- a/src/Test/Html/Internal/ElmHtml/Query.elm
+++ b/src/Test/Html/Internal/ElmHtml/Query.elm
@@ -263,8 +263,14 @@ hasStyle style facts =
 classnames : Facts msg -> List String
 classnames facts =
     (case ( Dict.get "class" facts.stringAttributes, Dict.get "className" facts.stringAttributes ) of
-        ( Just class, Just className ) ->
-            class ++ " " ++ className
+        ( Just _, Just _ ) ->
+            -- If you use both the `class` attribute and the `className` property at the same time,
+            -- it’s undefined which classes you end up with. It depends on which order they are specified,
+            -- which order elm/virtual-dom happens to apply them, and which of them changed most recently.
+            -- Mixing both is not a good idea. Ideally, we’d show some nice error message explaining this
+            -- here, but since this is very much an edge case it does not feel worth the complexity.
+            -- Instead, silently claim that there are no classes (that no classes match the node).
+            ""
 
         ( Just class, Nothing ) ->
             class
diff --git a/tests/src/Test/Html/QueryTests.elm b/tests/src/Test/Html/QueryTests.elm
index 3f8141dd..198d7b01 100644
--- a/tests/src/Test/Html/QueryTests.elm
+++ b/tests/src/Test/Html/QueryTests.elm
@@ -123,7 +123,7 @@ all =
                         divWithAttribute (Attr.property "className" (Encode.string "hello"))
                             |> Query.fromHtml
                             |> Query.has [ class "hello" ]
-                , test "matches one class added using Attr.attribute and one added using Attr.property" <|
+                , test "matches nothing if classes are added both using Attr.attribute and Attr.property" <|
                     \() ->
                         Html.div
                             [ Attr.attribute "class" "hello"
@@ -131,7 +131,9 @@ all =
                             ]
                             []
                             |> Query.fromHtml
-                            |> Query.has [ class "hello", class "world" ]
+                            |> Query.has [ class "hello" ]
+                            |> expectationToIsPassing
+                            |> Expect.equal False
                 ]
             ]
         , describe "Query.contains" <|