Give a nicer error message when under is passed empty

src/Review/Test.elm

@@ -841,16 +841,16 @@ checkErrorsMatch runResult expectedErrors errors =
 checkErrorMatch : CodeInspector -> ExpectedError -> Error -> (() -> Expectation)
 checkErrorMatch codeInspector ((ExpectedError expectedError_) as expectedError) error_ =
     Expect.all
-        [ (expectedError_.message == Rule.errorMessage error_)
+        [ \() ->
+            (expectedError_.message == Rule.errorMessage error_)
                 |> Expect.true
                     (ErrorMessage.messageMismatch
                         (extractExpectedErrorData expectedError)
                         error_
                     )
-            |> always
         , checkMessageAppearsUnder codeInspector error_ expectedError
         , checkDetailsAreCorrect error_ expectedError
-        , always <| checkFixesAreCorrect codeInspector error_ expectedError
+        , \() -> checkFixesAreCorrect codeInspector error_ expectedError
         ]
 
 
@@ -861,27 +861,37 @@ checkMessageAppearsUnder codeInspector error_ (ExpectedError expectedError) =
             case expectedError.under of
                 Under under ->
                     Expect.all
-                        [ (codeAtLocation == under)
+                        [ \() ->
+                            case under of
+                                "" ->
+                                    ErrorMessage.underMayNotBeEmpty
+                                        { message = expectedError.message
+                                        , codeAtLocation = codeAtLocation
+                                        }
+                                        |> Expect.fail
+
+                                _ ->
+                                    Expect.pass
+                        , \() ->
+                            (codeAtLocation == under)
                                 |> Expect.true (ErrorMessage.underMismatch error_ { under = under, codeAtLocation = codeAtLocation })
-                            |> always
-                        , codeInspector.checkIfLocationIsAmbiguous error_ under
-                            |> always
+                        , \() -> codeInspector.checkIfLocationIsAmbiguous error_ under
                         ]
 
                 UnderExactly under range ->
                     Expect.all
-                        [ (codeAtLocation == under)
+                        [ \() ->
+                            (codeAtLocation == under)
                                 |> Expect.true (ErrorMessage.underMismatch error_ { under = under, codeAtLocation = codeAtLocation })
-                            |> always
-                        , (Rule.errorRange error_ == range)
+                        , \() ->
+                            (Rule.errorRange error_ == range)
                                 |> Expect.true (ErrorMessage.wrongLocation error_ range under)
-                            |> always
                         ]
 
         Nothing ->
+            \() ->
                 ErrorMessage.locationNotFound error_
                     |> Expect.fail
-                |> always
 
 
 checkDetailsAreCorrect : Error -> ExpectedError -> (() -> Expectation)

src/Review/Test/ErrorMessage.elm

@@ -1,7 +1,7 @@
 module Review.Test.ErrorMessage exposing
     ( ExpectedErrorData
     , parsingFailure, messageMismatch, emptyDetails, unexpectedDetails, wrongLocation, didNotExpectErrors
-    , underMismatch, expectedMoreErrors, tooManyErrors, locationNotFound, locationIsAmbiguousInSourceCode
+    , underMismatch, expectedMoreErrors, tooManyErrors, locationNotFound, underMayNotBeEmpty, locationIsAmbiguousInSourceCode
     , needToUsedExpectErrorsForModules, duplicateModuleName, unknownModulesInExpectedErrors
     , missingFixes, unexpectedFixes, fixedCodeMismatch, unchangedSourceAfterFix, invalidSourceAfterFix, hasCollisionsInFixRanges
     )
@@ -13,7 +13,7 @@ module Review.Test.ErrorMessage exposing
 
 @docs ExpectedErrorData
 @docs parsingFailure, messageMismatch, emptyDetails, unexpectedDetails, wrongLocation, didNotExpectErrors
-@docs underMismatch, expectedMoreErrors, tooManyErrors, locationNotFound, locationIsAmbiguousInSourceCode
+@docs underMismatch, expectedMoreErrors, tooManyErrors, locationNotFound, underMayNotBeEmpty, locationIsAmbiguousInSourceCode
 @docs needToUsedExpectErrorsForModules, duplicateModuleName, unknownModulesInExpectedErrors
 @docs missingFixes, unexpectedFixes, fixedCodeMismatch, unchangedSourceAfterFix, invalidSourceAfterFix, hasCollisionsInFixRanges
 
@@ -232,6 +232,23 @@ Please try to have the error under the smallest region that makes sense.
 This will be the most helpful for the person who reads the error message."""
 
 
+underMayNotBeEmpty : { message : String, codeAtLocation : String } -> String
+underMayNotBeEmpty { message, codeAtLocation } =
+    """COULD NOT FIND LOCATION FOR ERROR
+
+I was looking for the error with the following message:
+
+  """ ++ wrapInQuotes message ++ """
+
+and I found it, but the expected error has an empty string for `under`. I
+need to point somewhere, so as to best help the people who encounter this
+error.
+
+If this helps, this is where I found the error:
+
+  """ ++ formatSourceCode codeAtLocation
+
+
 locationIsAmbiguousInSourceCode : SourceCode -> Error -> String -> List Int -> String
 locationIsAmbiguousInSourceCode sourceCode error under occurrencesInSourceCode =
     """AMBIGUOUS ERROR LOCATION

tests/ErrorMessageTest.elm

@@ -18,6 +18,7 @@ all =
         , unexpectedDetailsTest
         , emptyDetailsTest
         , wrongLocationTest
+        , underMayNotBeEmptyTest
         , locationNotFoundTest
         , expectedMoreErrorsTest
         , tooManyErrorsTest
@@ -458,6 +459,31 @@ This will be the most helpful for the person who reads the error message.
 """
 
 
+underMayNotBeEmptyTest : Test
+underMayNotBeEmptyTest =
+    test "underMayNotBeEmpty" <|
+        \() ->
+            ErrorMessage.underMayNotBeEmpty
+                { message = "Some error"
+                , codeAtLocation = "abcd = 1"
+                }
+                |> expectMessageEqual """
+COULD NOT FIND LOCATION FOR ERROR
+
+I was looking for the error with the following message:
+
+  `Some error`
+
+and I found it, but the expected error has an empty string for `under`. I
+need to point somewhere, so as to best help the people who encounter this
+error.
+
+If this helps, this is where I found the error:
+
+  `abcd = 1`
+"""
+
+
 expectedMoreErrorsTest : Test
 expectedMoreErrorsTest =
     test "expectedMoreErrors" <|