Fix operator in ValidationResult toString (#286)

Fixes #285 

This fixes the check for field path elements when calculating the
`toString` value for `ValidationResult` and adds a few tests.

Note that this also changes the value to print `Validation OK` if there
are no violations since it didn't make much sense to print `Validation
Error:` if there are no violations.

Technically this is a breaking change.

Author: smaye81

src/main/java/build/buf/protovalidate/ValidationResult.java

@@ -68,16 +68,20 @@ public List<Violation> getViolations() {
   @Override
   public String toString() {
     StringBuilder builder = new StringBuilder();
-    builder.append("Validation error:");
-    for (Violation violation : violations) {
-      builder.append("\n - ");
-      if (!violation.toProto().hasField()) {
-        builder.append(FieldPathUtils.fieldPathString(violation.toProto().getField()));
-        builder.append(": ");
+    if (isSuccess()) {
+      builder.append("Validation OK");
+    } else {
+      builder.append("Validation error:");
+      for (Violation violation : violations) {
+        builder.append("\n - ");
+        if (violation.toProto().hasField()) {
+          builder.append(FieldPathUtils.fieldPathString(violation.toProto().getField()));
+          builder.append(": ");
+        }
+        builder.append(
+            String.format(
+                "%s [%s]", violation.toProto().getMessage(), violation.toProto().getRuleId()));
       }
-      builder.append(
-          String.format(
-              "%s [%s]", violation.toProto().getMessage(), violation.toProto().getRuleId()));
     }
     return builder.toString();
   }

src/test/java/build/buf/protovalidate/ValidationResultTest.java

@@ -0,0 +1,123 @@
+// Copyright 2023-2024 Buf Technologies, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package build.buf.protovalidate;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import build.buf.validate.FieldPathElement;
+import java.util.ArrayList;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+class ValidationResultTest {
+  @Test
+  void testToStringNoViolations() {
+
+    List<Violation> violations = new ArrayList<Violation>();
+    ValidationResult result = new ValidationResult(violations);
+
+    assertThat(result.toString()).isEqualTo("Validation OK");
+    assertThat(result.isSuccess()).isTrue();
+  }
+
+  @Test
+  void testToStringSingleViolation() {
+    FieldPathElement elem =
+        FieldPathElement.newBuilder().setFieldNumber(5).setFieldName("test_field_name").build();
+
+    RuleViolation violation =
+        RuleViolation.newBuilder()
+            .setRuleId("int32.const")
+            .setMessage("value must equal 42")
+            .addFirstFieldPathElement(elem)
+            .build();
+    List<Violation> violations = new ArrayList<Violation>();
+    violations.add(violation);
+    ValidationResult result = new ValidationResult(violations);
+
+    assertThat(result.toString())
+        .isEqualTo("Validation error:\n - test_field_name: value must equal 42 [int32.const]");
+  }
+
+  @Test
+  void testToStringMultipleViolations() {
+    FieldPathElement elem =
+        FieldPathElement.newBuilder().setFieldNumber(5).setFieldName("test_field_name").build();
+
+    RuleViolation violation1 =
+        RuleViolation.newBuilder()
+            .setRuleId("int32.const")
+            .setMessage("value must equal 42")
+            .addFirstFieldPathElement(elem)
+            .build();
+
+    RuleViolation violation2 =
+        RuleViolation.newBuilder()
+            .setRuleId("int32.required")
+            .setMessage("value is required")
+            .addFirstFieldPathElement(elem)
+            .build();
+    List<Violation> violations = new ArrayList<Violation>();
+    violations.add(violation1);
+    violations.add(violation2);
+    ValidationResult result = new ValidationResult(violations);
+
+    assertThat(result.toString())
+        .isEqualTo(
+            "Validation error:\n - test_field_name: value must equal 42 [int32.const]\n - test_field_name: value is required [int32.required]");
+  }
+
+  @Test
+  void testToStringSingleViolationMultipleFieldPathElements() {
+    FieldPathElement elem1 =
+        FieldPathElement.newBuilder().setFieldNumber(5).setFieldName("test_field_name").build();
+    FieldPathElement elem2 =
+        FieldPathElement.newBuilder().setFieldNumber(5).setFieldName("nested_name").build();
+
+    List<FieldPathElement> elems = new ArrayList<FieldPathElement>();
+    elems.add(elem1);
+    elems.add(elem2);
+
+    RuleViolation violation1 =
+        RuleViolation.newBuilder()
+            .setRuleId("int32.const")
+            .setMessage("value must equal 42")
+            .addAllFieldPathElements(elems)
+            .build();
+
+    List<Violation> violations = new ArrayList<Violation>();
+    violations.add(violation1);
+    ValidationResult result = new ValidationResult(violations);
+
+    assertThat(result.toString())
+        .isEqualTo(
+            "Validation error:\n - test_field_name.nested_name: value must equal 42 [int32.const]");
+  }
+
+  @Test
+  void testToStringSingleViolationNoFieldPathElements() {
+    RuleViolation violation =
+        RuleViolation.newBuilder()
+            .setRuleId("int32.const")
+            .setMessage("value must equal 42")
+            .build();
+    List<Violation> violations = new ArrayList<Violation>();
+    violations.add(violation);
+    ValidationResult result = new ValidationResult(violations);
+
+    assertThat(result.toString())
+        .isEqualTo("Validation error:\n - value must equal 42 [int32.const]");
+  }
+}