diff --git a/quickwit/quickwit-metastore/src/tests/shard.rs b/quickwit/quickwit-metastore/src/tests/shard.rs
index 5748975e776..0d3d1f1cb8f 100644
--- a/quickwit/quickwit-metastore/src/tests/shard.rs
+++ b/quickwit/quickwit-metastore/src/tests/shard.rs
@@ -20,7 +20,8 @@
 use quickwit_common::rand::append_random_suffix;
 use quickwit_config::{IndexConfig, SourceConfig};
 use quickwit_proto::metastore::{
-    AddSourceRequest, CreateIndexRequest, MetastoreService, OpenShardsRequest, OpenShardsSubrequest,
+    AddSourceRequest, CreateIndexRequest, EntityKind, MetastoreError, MetastoreService,
+    OpenShardsRequest, OpenShardsSubrequest,
 };
 use quickwit_proto::types::{IndexUid, SourceId};
 
@@ -29,18 +30,26 @@ use crate::tests::cleanup_index;
 use crate::{AddSourceRequestExt, CreateIndexRequestExt, FileBackedMetastore, MetastoreServiceExt};
 
 // TODO: Remove when `PostgresqlMetastore` implements Shard API.
-pub trait DisableShardTestSuite {
-    fn disable_shard_test_suite() -> bool {
-        false
+pub trait RunTests {
+    fn run_open_shards_test() -> bool {
+        true
+    }
+
+    fn run_other_tests() -> bool {
+        true
     }
 }
 
-impl DisableShardTestSuite for FileBackedMetastore {}
+impl RunTests for FileBackedMetastore {}
 
 #[cfg(feature = "postgres")]
-impl DisableShardTestSuite for crate::PostgresqlMetastore {
-    fn disable_shard_test_suite() -> bool {
-        true
+impl RunTests for crate::PostgresqlMetastore {
+    fn run_other_tests() -> bool {
+        false
+    }
+
+    fn run_open_shards_test() -> bool {
+        false
     }
 }
 
@@ -81,9 +90,9 @@ impl TestIndex {
 }
 
 pub async fn test_metastore_open_shards<
-    MetastoreUnderTest: MetastoreService + MetastoreServiceExt + DefaultForTest + DisableShardTestSuite,
+    MetastoreUnderTest: MetastoreService + MetastoreServiceExt + DefaultForTest + RunTests,
 >() {
-    if MetastoreUnderTest::disable_shard_test_suite() {
+    if !MetastoreUnderTest::run_open_shards_test() {
         return;
     }
     let mut metastore = MetastoreUnderTest::default_for_test().await;
@@ -95,12 +104,50 @@ pub async fn test_metastore_open_shards<
     )
     .await;
 
+    // Test empty request.
     let open_shards_request = OpenShardsRequest {
         subrequests: Vec::new(),
     };
     let open_shards_response = metastore.open_shards(open_shards_request).await.unwrap();
     assert!(open_shards_response.subresponses.is_empty());
 
+    // Test index not found.
+    let open_shards_request = OpenShardsRequest {
+        subrequests: vec![OpenShardsSubrequest {
+            index_uid: "index-does-not-exist:0".to_string(),
+            source_id: test_index.source_config.source_id.clone(),
+            leader_id: "test-ingester-foo".to_string(),
+            next_shard_id: 1,
+            ..Default::default()
+        }],
+    };
+    let error = metastore
+        .open_shards(open_shards_request)
+        .await
+        .unwrap_err();
+    assert!(
+        matches!(error, MetastoreError::NotFound(EntityKind::Index { index_id }) if index_id == "index-does-not-exist")
+    );
+
+    // Test source not found.
+    let open_shards_request = OpenShardsRequest {
+        subrequests: vec![OpenShardsSubrequest {
+            index_uid: test_index.index_uid.clone().into(),
+            source_id: "source-does-not-exist".to_string(),
+            leader_id: "test-ingester-foo".to_string(),
+            next_shard_id: 1,
+            ..Default::default()
+        }],
+    };
+    let error = metastore
+        .open_shards(open_shards_request)
+        .await
+        .unwrap_err();
+    assert!(
+        matches!(error, MetastoreError::NotFound(EntityKind::Source { source_id, ..}) if source_id == "source-does-not-exist")
+    );
+
+    // Test open shard #1.
     let open_shards_request = OpenShardsRequest {
         subrequests: vec![OpenShardsSubrequest {
             index_uid: test_index.index_uid.clone().into(),
@@ -125,6 +172,7 @@ pub async fn test_metastore_open_shards<
     assert_eq!(shard.shard_id, 1);
     assert_eq!(shard.leader_id, "test-ingester-foo");
 
+    // Test open shard #1 is idempotent.
     let open_shards_request = OpenShardsRequest {
         subrequests: vec![OpenShardsSubrequest {
             index_uid: test_index.index_uid.clone().into(),
@@ -138,19 +186,64 @@ pub async fn test_metastore_open_shards<
     assert_eq!(open_shards_response.subresponses.len(), 1);
 
     let subresponse = &open_shards_response.subresponses[0];
+    assert_eq!(subresponse.next_shard_id, 2);
     assert_eq!(subresponse.opened_shards.len(), 1);
 
     let shard = &subresponse.opened_shards[0];
     assert_eq!(shard.shard_id, 1);
     assert_eq!(shard.leader_id, "test-ingester-foo");
 
+    // Test open shard #2.
+    let open_shards_request = OpenShardsRequest {
+        subrequests: vec![OpenShardsSubrequest {
+            index_uid: test_index.index_uid.clone().into(),
+            source_id: test_index.source_config.source_id.clone(),
+            leader_id: "test-ingester-qux".to_string(),
+            next_shard_id: 2,
+            ..Default::default()
+        }],
+    };
+    let open_shards_response = metastore.open_shards(open_shards_request).await.unwrap();
+    assert_eq!(open_shards_response.subresponses.len(), 1);
+
+    let subresponse = &open_shards_response.subresponses[0];
+    assert_eq!(subresponse.index_uid, test_index.index_uid.as_str());
+    assert_eq!(subresponse.source_id, test_index.source_config.source_id);
+    assert_eq!(subresponse.next_shard_id, 3);
+    assert_eq!(subresponse.opened_shards.len(), 1);
+
+    let shard = &subresponse.opened_shards[0];
+    assert_eq!(shard.index_uid, test_index.index_uid.as_str());
+    assert_eq!(shard.source_id, test_index.source_config.source_id);
+    assert_eq!(shard.shard_id, 2);
+    assert_eq!(shard.leader_id, "test-ingester-qux");
+
+    // Test open shard should not be called with a lagging `next_shard_id`.
+    let open_shards_request = OpenShardsRequest {
+        subrequests: vec![OpenShardsSubrequest {
+            index_uid: test_index.index_uid.clone().into(),
+            source_id: test_index.source_config.source_id.clone(),
+            leader_id: "test-ingester-foo".to_string(),
+            next_shard_id: 1,
+            ..Default::default()
+        }],
+    };
+    let error = metastore
+        .open_shards(open_shards_request)
+        .await
+        .unwrap_err();
+    assert!(matches!(
+        error,
+        MetastoreError::InconsistentControlPlaneState
+    ));
+
     cleanup_index(&mut metastore, test_index.index_uid).await;
 }
 
 pub async fn test_metastore_acquire_shards<
-    MetastoreUnderTest: MetastoreService + MetastoreServiceExt + DefaultForTest + DisableShardTestSuite,
+    MetastoreUnderTest: MetastoreService + MetastoreServiceExt + DefaultForTest + RunTests,
 >() {
-    if MetastoreUnderTest::disable_shard_test_suite() {
+    if !MetastoreUnderTest::run_other_tests() {
         return;
     }
     let mut metastore = MetastoreUnderTest::default_for_test().await;
@@ -168,9 +261,9 @@ pub async fn test_metastore_acquire_shards<
 }
 
 pub async fn test_metastore_list_shards<
-    MetastoreUnderTest: MetastoreService + MetastoreServiceExt + DefaultForTest + DisableShardTestSuite,
+    MetastoreUnderTest: MetastoreService + MetastoreServiceExt + DefaultForTest + RunTests,
 >() {
-    if MetastoreUnderTest::disable_shard_test_suite() {
+    if !MetastoreUnderTest::run_other_tests() {
         return;
     }
     let mut metastore = MetastoreUnderTest::default_for_test().await;
@@ -188,9 +281,9 @@ pub async fn test_metastore_list_shards<
 }
 
 pub async fn test_metastore_delete_shards<
-    MetastoreUnderTest: MetastoreService + MetastoreServiceExt + DefaultForTest + DisableShardTestSuite,
+    MetastoreUnderTest: MetastoreService + MetastoreServiceExt + DefaultForTest + RunTests,
 >() {
-    if MetastoreUnderTest::disable_shard_test_suite() {
+    if !MetastoreUnderTest::run_other_tests() {
         return;
     }
     let mut metastore = MetastoreUnderTest::default_for_test().await;