fix: server errors and related unit tests

Author: jmarkerink

core/src/main/java/de/bwaldvogel/mongo/backend/aggregation/Expression.java

@@ -1431,14 +1431,14 @@ Object apply(Object expressionValue, Document document) {
 
             // Validate that 'branches' field exists
             if (!switchDocument.containsKey("branches")) {
-                throw new MongoServerError(40061, "Missing 'branches' parameter to " + name());
+                throw new MongoServerError(40068, name() + " requires at least one branch");
             }
 
             // Validate unsupported parameters
             List<String> supportedKeys = asList("branches", "default");
             for (String key : switchDocument.keySet()) {
                 if (!supportedKeys.contains(key)) {
-                    throw new MongoServerError(40067, "Unrecognized parameter to " + name() + ": " + key);
+                    throw new MongoServerError(40067, name() + " found an unknown argument: " + key);
                 }
             }
 

test-common/src/main/java/de/bwaldvogel/mongo/backend/AbstractAggregationTest.java

@@ -2830,7 +2830,28 @@ void testAggregateWithSwitchMissingBranches() throws Exception {
 
         assertThatExceptionOfType(MongoCommandException.class)
             .isThrownBy(() -> collection.aggregate(pipeline).first())
-            .withMessageContaining("Missing 'branches' parameter to $switch");
+            .withMessageContaining("$switch requires at least one branch");
+    }
+
+    @Test
+    void testAggregateWithSwitchEmptyBranches() throws Exception {
+        collection.insertOne(json("_id: 1, value: 100"));
+
+        List<Document> pipeline = jsonList("""
+            $project: {
+              result: {
+                $switch: {
+                  branches: [
+                  ],
+                  default: 'none'
+                }
+              }
+            }
+            """);
+
+        assertThatExceptionOfType(MongoCommandException.class)
+            .isThrownBy(() -> collection.aggregate(pipeline).first())
+            .withMessageContaining("$switch requires at least one branch");
     }
 
     @Test
@@ -2855,6 +2876,28 @@ void testAggregateWithSwitchInvalidBranch() throws Exception {
             .withMessageContaining("$switch requires each branch have a 'then' expression");
     }
 
+    @Test
+    void testAggregateWithSwitchInvalidArgument() throws Exception {
+        collection.insertOne(json("_id: 1, value: 100"));
+
+        List<Document> pipeline = jsonList("""
+            $project: {
+              result: {
+                $switch: {
+                  branches: [
+                    { case: { $eq: ['$value', 100] }, then: 'one hundred' }
+                  ],
+                  default_value: 'none'
+                }
+              }
+            }
+            """);
+
+        assertThatExceptionOfType(MongoCommandException.class)
+            .isThrownBy(() -> collection.aggregate(pipeline).first())
+            .withMessageContaining("$switch found an unknown argument: default_value");
+    }
+
     // https://github.com/bwaldvogel/mongo-java-server/issues/138
     @Test
     public void testAggregateWithGeoNear() throws Exception {