add docs and spec for helpfully disabled button

src/Nri/Ui/Button/V10.elm

@@ -39,7 +39,10 @@ The next version of `Button` should also remove `delete` and `toggleButton`
   - adds `tertiary` style
   - adds `submit` and `opensModal`
   - adds `secondaryDanger` style
-  - marked toggleButton as deprecated and added toggleButtonPressed attribute
+  - marks toggleButton as deprecated and adds toggleButtonPressed attribute
+  - replaces the `disabled` attribute with `aria-disabled="true"`
+  - removes click handler from disabled buttons
+  - prevents default behavior for disabled submit buttons by setting `type="button"`
 
 
 # Changes from V9:

tests/Spec/Nri/Ui/Button.elm

@@ -1,17 +1,20 @@
 module Spec.Nri.Ui.Button exposing (spec)
 
 import Accessibility.Aria as Aria
+import Expect exposing (Expectation)
 import Html.Styled exposing (Html, toUnstyled)
 import Nri.Ui.Button.V10 as Button
 import ProgramTest exposing (..)
 import Test exposing (..)
 import Test.Html.Selector exposing (..)
+import Test.Runner
 
 
 spec : Test
 spec =
     describe "Nri.Ui.Button.V10"
         [ describe "toggleButtonPressed" toggleButtonPressed
+        , describe "helpfullyDisabledButton" helpfullyDisabledButton
         ]
 
 
@@ -35,6 +38,63 @@ toggleButtonPressed =
     ]
 
 
+expectFailure : String -> Expectation -> Expectation
+expectFailure expectedDescriptionSubstring expectation =
+    case Test.Runner.getFailureReason expectation of
+        Nothing ->
+            Expect.fail "Expected a failure, but there was none."
+
+        Just reason ->
+            String.contains expectedDescriptionSubstring reason.description
+                |> Expect.equal True
+
+
+helpfullyDisabledButton : List Test
+helpfullyDisabledButton =
+    [ test "does not have `aria-disabled=\"true\" when not disabled" <|
+        \() ->
+            program ()
+                (\_ ->
+                    Button.button "Italic"
+                        []
+                )
+                |> ensureViewHasNot [ attribute (Aria.disabled True) ]
+                |> done
+    , test "has `aria-disabled=\"true\" when disabled" <|
+        \() ->
+            program ()
+                (\_ ->
+                    Button.button "Italic"
+                        [ Button.disabled
+                        ]
+                )
+                |> ensureViewHas [ attribute (Aria.disabled True) ]
+                |> done
+    , test "is clickable when not disabled" <|
+        \() ->
+            program ()
+                (\_ ->
+                    Button.button "Italic"
+                        [ Button.onClick ()
+                        ]
+                )
+                |> clickButton "Italic"
+                |> done
+    , test "is not clickable when disabled" <|
+        \() ->
+            program ()
+                (\_ ->
+                    Button.button "Italic"
+                        [ Button.onClick ()
+                        , Button.disabled
+                        ]
+                )
+                |> clickButton "Italic"
+                |> done
+                |> expectFailure "Event.expectEvent: I found a node, but it does not listen for \"click\" events like I expected it would."
+    ]
+
+
 program : model -> (model -> Html model) -> ProgramTest model model ()
 program init view =
     ProgramTest.createSandbox