Improve message for invalid .errors entries

Author: kstich

config/spotbugs/filter.xml

@@ -149,6 +149,12 @@
         <Bug pattern="NP_NULL_ON_SOME_PATH_FROM_RETURN_VALUE"/>
     </Match>
 
+    <!-- This is a false positive. The value is guarded behind an Objects.requireNonNull -->
+    <Match>
+        <Class name="software.amazon.smithy.model.validation.testrunner.SmithyTestCase"/>
+        <Bug pattern="NP_NULL_ON_SOME_PATH_FROM_RETURN_VALUE"/>
+    </Match>
+
     <!-- We don't care about the return value of putIfAbsent in this cache -->
     <Match>
         <Class name="software.amazon.smithy.model.shapes.ShapeId$ShapeIdFactory"/>

smithy-model/src/main/java/software/amazon/smithy/model/validation/testrunner/SmithyTestCase.java

@@ -15,6 +15,9 @@
 
 package software.amazon.smithy.model.validation.testrunner;
 
+import static java.lang.String.format;
+
+import java.nio.file.Paths;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
@@ -164,16 +167,19 @@ private static String inferErrorFileLocation(String modelLocation) {
 
     private static List<ValidationEvent> loadExpectedEvents(String errorsFileLocation) {
         String contents = IoUtils.readUtf8File(errorsFileLocation);
+        String fileName = Objects.requireNonNull(Paths.get(errorsFileLocation).getFileName()).toString();
         return Arrays.stream(contents.split(System.lineSeparator()))
                 .filter(line -> !line.trim().isEmpty())
-                .map(SmithyTestCase::parseValidationEvent)
+                .map(line -> parseValidationEvent(line, fileName))
                 .collect(Collectors.toList());
     }
 
-    static ValidationEvent parseValidationEvent(String event) {
+    static ValidationEvent parseValidationEvent(String event, String fileName) {
         Matcher matcher = EVENT_PATTERN.matcher(event);
         if (!matcher.find()) {
-            throw new IllegalArgumentException("Invalid validation event: " + event);
+            throw new IllegalArgumentException(format("Invalid validation event in file `%s`, the following event did "
+                    + "not match the expected regular expression `%s`: %s",
+                    fileName, EVENT_PATTERN.pattern(), event));
         }
 
         // Construct a dummy source location since we don't validate it.

smithy-model/src/test/java/software/amazon/smithy/model/validation/testrunner/SmithyTestCaseTest.java

@@ -18,6 +18,7 @@
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.is;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.util.Collections;
 import org.junit.jupiter.api.Assertions;
@@ -32,14 +33,17 @@
 public class SmithyTestCaseTest {
     @Test
     public void validatesThatEventsAreValid() {
-        Assertions.assertThrows(
+        IllegalArgumentException e = Assertions.assertThrows(
                 IllegalArgumentException.class,
-                () -> SmithyTestCase.parseValidationEvent("[ERROR] - m"));
+                () -> SmithyTestCase.parseValidationEvent("[ERROR] - m", "filename"));
+
+        assertTrue(e.getMessage().contains("`filename`"));
+        assertTrue(e.getMessage().contains("SUPPRESSED|NOTE|WARNING|DANGER|ERROR"));
     }
 
     @Test
     public void parsesValidEvents() {
-        SmithyTestCase.parseValidationEvent("[ERROR] -: message | EventId /filename:0:0");
+        SmithyTestCase.parseValidationEvent("[ERROR] -: message | EventId /filename:0:0", "filename");
     }
 
     @Test