Properly handle average confidence for translation jos with no pretranslations (#991)

Author: Enkidu93

src/Serval/src/Serval.Translation/Services/PlatformService.cs

@@ -376,7 +376,7 @@ public async Task InsertPretranslationsAsync(
         int nextModelRevision = engine.ModelRevision + 1;
 
         var batch = new List<Pretranslation>();
-        double confidenceTotal = 0.0;
+        double totalConfidence = 0.0;
         int numPretranslations = 0;
         await foreach (PretranslationContract item in pretranslations.WithCancellation(cancellationToken))
         {
@@ -404,7 +404,7 @@ public async Task InsertPretranslationsAsync(
                     Confidence = item.Confidence,
                 }
             );
-            confidenceTotal += item.Confidence ?? 0.0;
+            totalConfidence += item.Confidence ?? 0.0;
             numPretranslations += 1;
             if (batch.Count == PretranslationInsertBatchSize)
             {
@@ -417,7 +417,11 @@ public async Task InsertPretranslationsAsync(
 
         await _builds.UpdateAsync(
             b => b.Id == buildId,
-            u => u.Set(b => b.ExecutionData.AveragePretranslationConfidence, confidenceTotal / numPretranslations),
+            u =>
+                u.Set(
+                    b => b.ExecutionData.AveragePretranslationConfidence,
+                    numPretranslations > 0 ? totalConfidence / numPretranslations : 0.0
+                ),
             cancellationToken: cancellationToken
         );
     }

src/Serval/test/Serval.Translation.Tests/Services/PlatformServiceTests.cs

@@ -52,13 +52,27 @@ await env.Builds.InsertAsync(
         Assert.That(env.Pretranslations.Count, Is.EqualTo(1));
         await env.PlatformService.BuildCompletedAsync("b0", 0, 0.0);
         Assert.That(env.Pretranslations.Count, Is.EqualTo(1));
+
         await env.PlatformService.BuildStartedAsync("b0");
         await env.PlatformService.InsertPretranslationsAsync("e0", "b0", GetTestPretranslations());
         await env.PlatformService.BuildCompletedAsync("b0", 0, 0.0);
         Assert.That(env.Pretranslations.Count, Is.EqualTo(1));
         Assert.That(
             (await env.Builds.GetAsync(b => b.Id == "b0"))?.ExecutionData.AveragePretranslationConfidence,
-            Is.Zero
+            Is.Zero.Within(0.001)
+        );
+
+        await env.PlatformService.BuildStartedAsync("b0");
+        await env.PlatformService.InsertPretranslationsAsync(
+            "e0",
+            "b0",
+            AsyncEnumerable.Empty<PretranslationContract>()
+        );
+        await env.PlatformService.BuildCompletedAsync("b0", 0, 0.0);
+        Assert.That(env.Pretranslations.Count, Is.EqualTo(0));
+        Assert.That(
+            (await env.Builds.GetAsync(b => b.Id == "b0"))?.ExecutionData.AveragePretranslationConfidence,
+            Is.Zero.Within(0.001)
         );
     }