diff --git a/plugin/trino-iceberg/src/test/java/io/trino/plugin/iceberg/BaseIcebergConnectorTest.java b/plugin/trino-iceberg/src/test/java/io/trino/plugin/iceberg/BaseIcebergConnectorTest.java
index 3e3a00645da9..171cb711510e 100644
--- a/plugin/trino-iceberg/src/test/java/io/trino/plugin/iceberg/BaseIcebergConnectorTest.java
+++ b/plugin/trino-iceberg/src/test/java/io/trino/plugin/iceberg/BaseIcebergConnectorTest.java
@@ -4949,7 +4949,7 @@ public void testOptimize(int formatVersion)
         int workerCount = getQueryRunner().getNodeCount();
 
         // optimize an empty table
-        assertQuerySucceeds("ALTER TABLE " + tableName + " EXECUTE OPTIMIZE");
+        assertQuerySucceeds(withSingleWriterPerTask(getSession()), "ALTER TABLE " + tableName + " EXECUTE OPTIMIZE");
         assertThat(getActiveFiles(tableName)).isEmpty();
 
         assertUpdate("INSERT INTO " + tableName + " VALUES (11, 'eleven')", 1);
@@ -4964,7 +4964,8 @@ public void testOptimize(int formatVersion)
                 // Verify we have sufficiently many test rows with respect to worker count.
                 .hasSizeGreaterThan(workerCount);
 
-        computeActual("ALTER TABLE " + tableName + " EXECUTE OPTIMIZE");
+        // For optimize we need to set task_writer_count to 1, otherwise it will create more than one file.
+        computeActual(withSingleWriterPerTask(getSession()), "ALTER TABLE " + tableName + " EXECUTE OPTIMIZE");
         assertThat(query("SELECT sum(key), listagg(value, ' ') WITHIN GROUP (ORDER BY key) FROM " + tableName))
                 .matches("VALUES (BIGINT '65', VARCHAR 'eleven zwölf trzynaście quatorze пʼятнадцять')");
         List<String> updatedFiles = getActiveFiles(tableName);
@@ -4976,7 +4977,8 @@ public void testOptimize(int formatVersion)
                 .containsExactlyInAnyOrderElementsOf(concat(initialFiles, updatedFiles));
 
         // optimize with low retention threshold, nothing should change
-        computeActual("ALTER TABLE " + tableName + " EXECUTE OPTIMIZE (file_size_threshold => '33B')");
+        // For optimize we need to set task_writer_count to 1, otherwise it will create more than one file.
+        computeActual(withSingleWriterPerTask(getSession()), "ALTER TABLE " + tableName + " EXECUTE OPTIMIZE (file_size_threshold => '33B')");
         assertThat(query("SELECT sum(key), listagg(value, ' ') WITHIN GROUP (ORDER BY key) FROM " + tableName))
                 .matches("VALUES (BIGINT '65', VARCHAR 'eleven zwölf trzynaście quatorze пʼятнадцять')");
         assertThat(getActiveFiles(tableName)).isEqualTo(updatedFiles);
@@ -5006,7 +5008,7 @@ public void testOptimizeForPartitionedTable(int formatVersion)
         String tableName = "test_repartitiong_during_optimize_" + randomNameSuffix();
         assertUpdate(session, "CREATE TABLE " + tableName + " (key varchar, value integer) WITH (format_version = " + formatVersion + ", partitioning = ARRAY['key'])");
         // optimize an empty table
-        assertQuerySucceeds(session, "ALTER TABLE " + tableName + " EXECUTE OPTIMIZE");
+        assertQuerySucceeds(withSingleWriterPerTask(session), "ALTER TABLE " + tableName + " EXECUTE OPTIMIZE");
 
         assertUpdate(session, "INSERT INTO " + tableName + " VALUES ('one', 1)", 1);
         assertUpdate(session, "INSERT INTO " + tableName + " VALUES ('one', 2)", 1);
@@ -5022,7 +5024,8 @@ public void testOptimizeForPartitionedTable(int formatVersion)
         List<String> initialFiles = getActiveFiles(tableName);
         assertThat(initialFiles).hasSize(10);
 
-        computeActual(session, "ALTER TABLE " + tableName + " EXECUTE OPTIMIZE");
+        // For optimize we need to set task_writer_count to 1, otherwise it will create more than one file.
+        computeActual(withSingleWriterPerTask(session), "ALTER TABLE " + tableName + " EXECUTE OPTIMIZE");
 
         assertThat(query(session, "SELECT sum(value), listagg(key, ' ') WITHIN GROUP (ORDER BY key) FROM " + tableName))
                 .matches("VALUES (BIGINT '55', VARCHAR 'one one one one one one one three two two')");
@@ -5081,10 +5084,11 @@ public void testOptimizeTimePartitionedTable(String dataType, String partitionin
                 .isGreaterThanOrEqualTo(5);
 
         assertUpdate(
+                // For optimize we need to set task_writer_count to 1, otherwise it will create more than one file.
                 // Use UTC zone so that DATE and TIMESTAMP WITH TIME ZONE comparisons align with partition boundaries.
-                Session.builder(getSession())
+                withSingleWriterPerTask(Session.builder(getSession())
                         .setTimeZoneKey(UTC_KEY)
-                        .build(),
+                        .build()),
                 "ALTER TABLE " + tableName + " EXECUTE optimize WHERE p >= " + optimizeDate);
 
         assertThat((long) computeScalar("SELECT count(DISTINCT \"$path\") FROM " + tableName + " WHERE p < " + optimizeDate))
@@ -5096,9 +5100,10 @@ public void testOptimizeTimePartitionedTable(String dataType, String partitionin
 
         // Verify that WHERE CAST(p AS date) ... form works in non-UTC zone
         assertUpdate(
-                Session.builder(getSession())
+                // For optimize we need to set task_writer_count to 1, otherwise it will create more than one file.
+                withSingleWriterPerTask(Session.builder(getSession())
                         .setTimeZoneKey(getTimeZoneKey("Asia/Kathmandu"))
-                        .build(),
+                        .build()),
                 "ALTER TABLE " + tableName + " EXECUTE optimize WHERE CAST(p AS date) >= " + optimizeDate);
 
         // Table state shouldn't change substantially (but files may be rewritten)
@@ -5141,7 +5146,8 @@ public void testOptimizeTableAfterDeleteWithFormatVersion2()
                 "SELECT summary['total-delete-files'] FROM \"" + tableName + "$snapshots\" WHERE snapshot_id = " + getCurrentSnapshotId(tableName),
                 "VALUES '1'");
 
-        computeActual("ALTER TABLE " + tableName + " EXECUTE OPTIMIZE");
+        // For optimize we need to set task_writer_count to 1, otherwise it will create more than one file.
+        computeActual(withSingleWriterPerTask(getSession()), "ALTER TABLE " + tableName + " EXECUTE OPTIMIZE");
 
         List<String> updatedFiles = getActiveFiles(tableName);
         assertThat(updatedFiles)
@@ -5174,7 +5180,8 @@ public void testOptimizeCleansUpDeleteFiles()
         List<String> allDataFilesAfterDelete = getAllDataFilesFromTableDirectory(tableName);
         assertThat(allDataFilesAfterDelete).hasSize(6);
 
-        computeActual("ALTER TABLE " + tableName + " EXECUTE OPTIMIZE WHERE regionkey = 4");
+        // For optimize we need to set task_writer_count to 1, otherwise it will create more than one file.
+        computeActual(withSingleWriterPerTask(getSession()), "ALTER TABLE " + tableName + " EXECUTE OPTIMIZE WHERE regionkey = 4");
         computeActual(sessionWithShortRetentionUnlocked, "ALTER TABLE " + tableName + " EXECUTE EXPIRE_SNAPSHOTS (retention_threshold => '0s')");
         computeActual(sessionWithShortRetentionUnlocked, "ALTER TABLE " + tableName + " EXECUTE REMOVE_ORPHAN_FILES (retention_threshold => '0s')");
 
@@ -5190,7 +5197,8 @@ public void testOptimizeCleansUpDeleteFiles()
         assertThat(query("SELECT * FROM " + tableName))
                 .matches("SELECT * FROM nation WHERE nationkey != 7");
 
-        computeActual("ALTER TABLE " + tableName + " EXECUTE OPTIMIZE");
+        // For optimize we need to set task_writer_count to 1, otherwise it will create more than one file.
+        computeActual(withSingleWriterPerTask(getSession()), "ALTER TABLE " + tableName + " EXECUTE OPTIMIZE");
         computeActual(sessionWithShortRetentionUnlocked, "ALTER TABLE " + tableName + " EXECUTE EXPIRE_SNAPSHOTS (retention_threshold => '0s')");
         computeActual(sessionWithShortRetentionUnlocked, "ALTER TABLE " + tableName + " EXECUTE REMOVE_ORPHAN_FILES (retention_threshold => '0s')");