Add golden file tests

src/Elm/Kernel/Test.js

@@ -1,11 +1,11 @@
 /*
 
 import Elm.Kernel.Utils exposing (Tuple0)
+import File exposing (FileNotFound, GeneralFileError, IsDirectory, PathEscapesDirectory)
 import Result exposing (Err, Ok)
 
 */
 
-
 function _Test_runThunk(thunk)
 {
   try {
@@ -16,3 +16,71 @@ function _Test_runThunk(thunk)
     return __Result_Err(err.toString());
   }
 }
+
+
+const fs = require('fs');
+const path = require('path');
+
+function _Test_readFile(filePath)
+{
+    // Test for this early as `resolve` will strip training slashes
+    if (filePath.slice(-1) == path.sep) {
+        return __Result_Err(__File_IsDirectory);
+    }
+
+    // Protect against reading files above the "tests" directory
+    const testsPath = path.resolve("tests");
+    const fullPath = path.resolve(testsPath, filePath);
+
+    if (!fullPath.startsWith(testsPath))
+    {
+        return __Result_Err(__File_PathEscapesDirectory);
+    }
+
+    try {
+        return __Result_Ok(fs.readFileSync(fullPath, { encoding: 'utf8' }));
+    }
+    catch (err)
+    {
+        if (err.code == "ENOENT"){
+            return __Result_Err(__File_FileNotFound);
+        }
+        else {
+            return __Result_Err(__File_GeneralFileError(err.toString()));
+        }
+    }
+}
+
+var _Test_writeFile = F2(function(filePath, contents)
+{
+    // Test for this early as `resolve` will strip training slashes
+    if (filePath.slice(-1) == path.sep) {
+        return __Result_Err(__File_IsDirectory);
+    }
+
+    // Protect against writing files above the "tests" directory
+    const testsPath = path.resolve("tests");
+    const fullPath = path.resolve(testsPath, filePath);
+
+    if (!fullPath.startsWith(testsPath))
+    {
+        return __Result_Err(__File_PathEscapesDirectory);
+    }
+
+    const fullDir = path.dirname(fullPath);
+
+    if (!fs.existsSync(fullDir))
+    {
+        // Can this make a nested directory? 
+        fs.mkdirSync(fullDir, {recursive: true});
+    }
+
+    try {
+        fs.writeFileSync(fullPath, contents);
+        return __Result_Ok(__Utils_Tuple0);
+    }
+    catch (err)
+    {   
+        return __Result_Err(__File_GeneralFileError(err.toString()));
+    }
+})

src/Expect.elm

@@ -3,7 +3,7 @@ module Expect exposing
     , lessThan, atMost, greaterThan, atLeast
     , FloatingPointTolerance(..), within, notWithin
     , ok, err, equalLists, equalDicts, equalSets
-    , pass, fail, onFail
+    , pass, fail, onFail, equalToFile
     )
 
 {-| A library to create `Expectation`s, which describe a claim to be tested.
@@ -42,6 +42,9 @@ or both. For an in-depth look, see our [Guide to Floating Point Comparison](#gui
 
 @docs ok, err, equalLists, equalDicts, equalSets
 
+## Golden Files
+
+@docs equalToFile
 
 ## Customizing
 
@@ -104,6 +107,7 @@ Another example is comparing values that are on either side of zero. `0.0001` is
 
 import Dict exposing (Dict)
 import Set exposing (Set)
+import File
 import Test.Distribution
 import Test.Expectation
 import Test.Internal as Internal
@@ -576,6 +580,42 @@ equalSets expected actual =
         reportCollectionFailure "Expect.equalSets" expected actual missingKeys extraKeys
 
 
+{-| Tests the a String is equal to the contents of the file stored at the file path. 
+
+If the file does not exist, it will be created and this test will pass.
+
+If the file does exist, then this test will pass if its contents are equal to the actual string.
+
+All file paths are scoped to be within the "tests/" directory.
+
+-}
+equalToFile : String -> String -> Expectation
+equalToFile filePath actual =
+    case File.readFile filePath of 
+        Err File.FileNotFound ->
+            case File.writeFile filePath actual of 
+                Err (File.GeneralFileError fileError) -> 
+                    Test.Expectation.fail { description = "Expect.equalToFile encountered a general file error: " ++ fileError, reason = Custom }
+
+                -- This case should be impossible non general file errors should have been surfaced in the call to `readFile` above.
+                Err _ -> 
+                    Test.Expectation.fail { description = "Expect.equalToFile encountered an unexpected error", reason = Custom  }
+
+                Ok _ ->
+                    pass
+
+        Err File.IsDirectory -> 
+            Test.Expectation.fail { description = "Expect.equalToFile was given a directory instead of a file", reason = Custom }
+
+        Err File.PathEscapesDirectory -> 
+            Test.Expectation.fail { description = "Expect.equalToFile was given a path that would escape the tests/ directory", reason = Custom }
+
+        Err (File.GeneralFileError fileError) -> 
+            Test.Expectation.fail { description = "Expect.equalToFile encountered a general file error: " ++ fileError, reason = Custom }
+
+        Ok contents -> 
+            equateWith ("equalToFile \'" ++ filePath ++ "\'") (==) contents actual
+
 {-| Always passes.
 
     import Json.Decode exposing (decodeString, int)

src/File.elm

@@ -0,0 +1,15 @@
+module File exposing (readFile, writeFile, FileError(..))
+
+import Elm.Kernel.Test
+
+type FileError
+    = FileNotFound
+    | IsDirectory
+    | PathEscapesDirectory
+    | GeneralFileError String
+
+readFile : String -> Result FileError String
+readFile = Elm.Kernel.Test.readFile
+
+writeFile : String -> String -> Result FileError ()
+writeFile = Elm.Kernel.Test.writeFile

src/Test/Html/Query.elm

@@ -2,6 +2,7 @@ module Test.Html.Query exposing
     ( Single, Multiple, fromHtml
     , find, findAll, children, first, index, keep
     , count, contains, has, hasNot, each
+    , prettyPrintSingle
     )
 
 {-| Querying HTML structure.
@@ -18,6 +19,10 @@ module Test.Html.Query exposing
 
 @docs count, contains, has, hasNot, each
 
+## Debugging
+
+@docs prettyPrintSingle
+
 -}
 
 import Expect exposing (Expectation)
@@ -496,3 +501,16 @@ each : (Single msg -> Expectation) -> Multiple msg -> Expectation
 each check (Internal.Multiple showTrace query) =
     Internal.expectAll check query
         |> failWithQuery showTrace "Query.each" query
+
+{-| Pretty prints the result of a query as HTML if successful -}
+prettyPrintSingle : Single msg -> Result String String
+prettyPrintSingle (Internal.Single _ query) =
+    case Internal.traverse query of 
+        Ok [ element ] -> 
+            Ok <| Internal.prettyPrint element
+
+        Ok results -> 
+            Err <| "Query.prettyPrintSingle expected exactly one result from query, but found " ++ String.fromInt (List.length results)
+
+        Err queryError -> 
+            Err <| "Query.prettyPrintSingle " ++ Internal.queryErrorToString queryError