Test: Split long failure diagnostics without truncation

Renames and updates the DiscordReportFormatter test to validate splitting of large failure diagnostics instead of step results. The test now builds a small report with a failed step and a 2500-character diagnostic payload, invokes the formatter, collects messages containing the "Failure Diagnostics" field, and asserts that diagnostics are split across multiple messages, that all 2500 'z' characters are preserved, that the relevant step label (Step 3) appears, and that no truncation marker is present. Replaces previous assertions which targeted "Step Results".

Author: ahmetcelik05

src/Validator.Core.Tests/Reporter/DiscordReportFormatterTests.cs

@@ -11,25 +11,42 @@ namespace Validator.Core.Tests.Reporter;
 public class DiscordReportFormatterTests
 {
     [Fact]
-    public void FormatMessages_ShouldSplitLongStepResults_WithoutTruncationMarker()
+    public void FormatMessages_ShouldSplitLongFailureDiagnostics_WithoutTruncationMarker()
     {
-        var report = CreateReport(140);
-        var formatter = new DiscordReportFormatter();
+        var report = CreateReport(3);
+        report.Result.Status = ValidationStatus.Failed;
+        report.Result.PassedSteps = 2;
+        report.Result.FailedSteps = 1;
+        report.Result.FailedAtStepId = 3;
+        report.Result.StepResults[2].Status = StepExecutionStatus.Failed;
+        report.Result.StepResults[2].ErrorMessage = "error";
+        report.FailureDiagnostics =
+        [
+            new FailureDiagnostic
+            {
+                StepId = 3,
+                Classification = FailureClassification.Unknown,
+                Explanation = new string('z', 2500)
+            }
+        ];
 
+        var formatter = new DiscordReportFormatter();
         var messages = formatter.FormatMessages(report);
-        var stepMessages = messages
-            .Where(m => m.Embeds.Count > 0 && m.Embeds[0].Fields.Any(f => f.Name == "Step Results"))
+        var diagnosticsMessages = messages
+            .Where(m => m.Embeds.Count > 0 && m.Embeds[0].Fields.Any(f => f.Name == "Failure Diagnostics"))
             .ToList();
 
-        Assert.True(stepMessages.Count > 1);
+        Assert.True(diagnosticsMessages.Count > 1);
+
+        var fieldValues = diagnosticsMessages
+            .Select(m => m.Embeds[0].Fields.First(f => f.Name == "Failure Diagnostics").Value)
+            .ToList();
 
-        var allStepText = string.Join(
-            '\n',
-            stepMessages.Select(m => m.Embeds[0].Fields.First(f => f.Name == "Step Results").Value));
+        var allDiagnosticsText = string.Join('\n', fieldValues);
 
-        Assert.Contains("Step 1", allStepText);
-        Assert.Contains("Step 140", allStepText);
-        Assert.DoesNotContain("… (truncated)", allStepText);
+        Assert.Contains("Step 3", allDiagnosticsText);
+        Assert.Equal(2500, fieldValues.Sum(v => v.Count(c => c == 'z')));
+        Assert.DoesNotContain("… (truncated)", allDiagnosticsText);
     }
 
     [Fact]