test: Add tests for handling distinct query errors

Author: Chamika36

Diff for: tests/jballerina-unit-test/src/test/java/org/ballerinalang/test/query/QueryDistinctErrorTest.java

@@ -0,0 +1,50 @@
+/*
+ *  Copyright (c) 2021, WSO2 Inc. (http://www.wso2.org) All Rights Reserved.
+ *
+ *  WSO2 Inc. licenses this file to you 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 org.ballerinalang.test.query;
+
+import org.ballerinalang.test.BCompileUtil;
+import org.ballerinalang.test.BRunUtil;
+import org.ballerinalang.test.CompileResult;
+import org.testng.annotations.AfterClass;
+import org.testng.annotations.BeforeClass;
+import org.testng.annotations.Test;
+
+public class QueryDistinctErrorTest {
+    private CompileResult result;
+
+    @BeforeClass
+    public void setup() {
+        result = BCompileUtil.compile("test-src/query/query-distinct-error.bal");
+    }
+
+    @Test
+    public void testDistinctTypeMismatchError() {
+        BRunUtil.invoke(result, "testDistinctTypeMismatchError");
+    }
+
+    @Test
+    public void testQueryDistinctError() {
+        BRunUtil.invoke(result, "testQueryDistinctError");
+    }
+
+    @AfterClass
+    public void tearDown() {
+        result = null;
+    }
+}

Diff for: tests/jballerina-unit-test/src/test/resources/test-src/query/query-distinct-error.bal

@@ -0,0 +1,133 @@
+// Copyright (c) 2025 WSO2 Inc. (http://www.wso2.org) All Rights Reserved.
+//
+// WSO2 Inc. licenses this file to you 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.
+
+type Album record {
+    string id;
+    string name;
+    string artist;
+    decimal price;
+};
+
+type TypeMismatchError distinct error;
+
+class MockStream {
+    private boolean hasNext = true;
+
+    public isolated function next() returns record {| Album value; |}|error? {
+        if self.hasNext {
+            self.hasNext = false;
+            return error TypeMismatchError("Error when iterating the SQL result. invalid value for record field 'artist': expected value of type 'string', found '()'");
+        }
+        return ();
+    }
+}
+
+function createMockStream() returns stream<Album, error?> {
+    MockStream mockStream = new MockStream();
+    return new (mockStream);
+}
+
+public function testDistinctTypeMismatchError() {
+    stream<Album, error?> albumStream = createMockStream();
+
+    int count = 0;
+    error? e = from Album _ in albumStream do {
+        count = count + 1;
+    };
+
+    assertEquality(0, count);
+    assertTrue(e is TypeMismatchError);
+    if e is TypeMismatchError {
+        assertEquality(e.message(), "Error when iterating the SQL result. invalid value for record field 'artist': expected value of type 'string', found '()'");
+    }
+}
+
+class EvenNumberGenerator {
+    int i = 0;
+    public isolated function next() returns record {|int value;|}|error? {
+        self.i += 2;
+        if (self.i > 10) {
+            return error("No more even numbers available.");
+        }
+        return {value: self.i};
+    }
+}
+
+function testErrorFromQueryPipeline() returns string|error? {
+    EvenNumberGenerator evenGen = new ();
+    EvenNumberGenerator evenGen2 = new ();
+
+    stream<int, error?> evenNumberStream = new (evenGen);
+    stream<int, error?> evenNumberStream2 = new (evenGen2);
+
+    error? err = from var i in evenNumberStream 
+        do {
+            record {| int value; |}? result = check evenNumberStream2.next();
+            int? intResult = result?.value;
+        };
+
+    assertTrue(err is error);
+    return "should reach here";
+}
+
+function testErrorFromQueryBody() returns string|error? {
+    EvenNumberGenerator evenGen = new ();
+    EvenNumberGenerator evenGen2 = new ();
+
+    stream<int, error?> evenNumberStream = new (evenGen);
+    stream<int, error?> evenNumberStream2 = new (evenGen2);
+
+    error? err = from var i in 1...10
+        do {
+            record {| int value; |}? result = check evenNumberStream2.next();
+            int? intResult = result?.value;
+        };
+
+    assertTrue(err is error);
+    return "shouldn't reach here";
+}
+
+function testQueryDistinctError() {
+    assertEquality("should reach here", testErrorFromQueryPipeline());
+    assertTrue(testErrorFromQueryBody() is error);
+}
+
+// Assertions ---------------------------------------------------------------------------------------------------------
+
+const ASSERTION_ERROR_REASON = "AssertionError";
+
+function assertTrue(any|error actual) {
+    assertEquality(true, actual);
+}
+
+function assertEquality(any|error expected, any|error actual) {
+    if expected is anydata && actual is anydata && expected == actual {
+        return;
+    }
+
+    if expected === actual {
+        return;
+    }
+
+    string expectedValAsString = expected is error ? expected.toString() : expected.toString();
+    string actualValAsString = actual is error ? actual.toString() : actual.toString();
+    if expectedValAsString == actualValAsString {
+        return;
+    }
+
+    panic error(ASSERTION_ERROR_REASON,
+                            message = "expected '" + expectedValAsString + "', found '" + actualValAsString + "'");
+}