diff --git a/cli/tests/test_operations.rs b/cli/tests/test_operations.rs
index 84a1ea7a2..fb6b64374 100644
--- a/cli/tests/test_operations.rs
+++ b/cli/tests/test_operations.rs
@@ -68,35 +68,15 @@ fn test_op_log() {
     @  230dd059e1b059aefc0da06a2e5a7dbf22362f22
     ◉  0000000000000000000000000000000000000000
     "###);
-    insta::assert_snapshot!(get_log_output(&test_env, &repo_path, "@--"), @r###"
-    ◉  0000000000000000000000000000000000000000
-    "###);
     insta::assert_snapshot!(
         test_env.jj_cmd_failure(&repo_path, &["log", "--at-op", "@---"]), @r###"
     Error: The "@---" expression resolved to no operations
     "###);
-    // "ID-" also resolves to the parent.
-    insta::assert_snapshot!(
-        get_log_output(&test_env, &repo_path, &format!("{add_workspace_id}-")), @r###"
-    ◉  0000000000000000000000000000000000000000
-    "###);
 
     // We get a reasonable message if an invalid operation ID is specified
     insta::assert_snapshot!(test_env.jj_cmd_failure(&repo_path, &["log", "--at-op", "foo"]), @r###"
     Error: Operation ID "foo" is not a valid hexadecimal prefix
     "###);
-    // Odd length
-    insta::assert_snapshot!(test_env.jj_cmd_failure(&repo_path, &["log", "--at-op", "123456789"]), @r###"
-    Error: No operation ID matching "123456789"
-    "###);
-    // Even length
-    insta::assert_snapshot!(test_env.jj_cmd_failure(&repo_path, &["log", "--at-op", "0123456789"]), @r###"
-    Error: No operation ID matching "0123456789"
-    "###);
-    // Empty ID
-    insta::assert_snapshot!(test_env.jj_cmd_failure(&repo_path, &["log", "--at-op", ""]), @r###"
-    Error: Operation ID "" is not a valid hexadecimal prefix
-    "###);
 
     test_env.jj_cmd_ok(&repo_path, &["describe", "-m", "description 1"]);
     test_env.jj_cmd_ok(
@@ -112,10 +92,6 @@ fn test_op_log() {
     insta::assert_snapshot!(test_env.jj_cmd_failure(&repo_path, &["log", "--at-op", "@-"]), @r###"
     Error: The "@" expression resolved to more than one operation
     "###);
-    test_env.jj_cmd_ok(&repo_path, &["st"]);
-    insta::assert_snapshot!(test_env.jj_cmd_failure(&repo_path, &["log", "--at-op", "@-"]), @r###"
-    Error: The "@-" expression resolved to more than one operation
-    "###);
 }
 
 #[test]
diff --git a/lib/tests/test_operations.rs b/lib/tests/test_operations.rs
index 3e41b0a81..b85dcfc6a 100644
--- a/lib/tests/test_operations.rs
+++ b/lib/tests/test_operations.rs
@@ -14,8 +14,12 @@
 
 use std::path::Path;
 
+use assert_matches::assert_matches;
+use itertools::Itertools as _;
 use jj_lib::backend::{CommitId, ObjectId};
+use jj_lib::op_walk::{self, OpsetEvaluationError, OpsetResolutionError};
 use jj_lib::repo::Repo;
+use jj_lib::settings::UserSettings;
 use testutils::{create_random_commit, write_random_commit, TestRepo};
 
 fn list_dir(dir: &Path) -> Vec<String> {
@@ -177,3 +181,125 @@ fn test_isolation() {
     let repo = repo.reload_at_head(&settings).unwrap();
     assert_heads(repo.as_ref(), vec![rewrite1.id(), rewrite2.id()]);
 }
+
+fn stable_op_id_settings() -> UserSettings {
+    UserSettings::from_config(
+        testutils::base_config()
+            .add_source(config::File::from_str(
+                "debug.operation-timestamp = '2001-02-03T04:05:06+07:00'",
+                config::FileFormat::Toml,
+            ))
+            .build()
+            .unwrap(),
+    )
+}
+
+#[test]
+fn test_resolve_op_id() {
+    let settings = stable_op_id_settings();
+    let test_repo = TestRepo::init_with_settings(&settings);
+    let mut repo = test_repo.repo;
+
+    let mut operations = Vec::new();
+    for i in 0..6 {
+        let tx = repo.start_transaction(&settings);
+        repo = tx.commit(format!("transaction {i}"));
+        operations.push(repo.operation().clone());
+    }
+    // "2" is ambiguous
+    insta::assert_debug_snapshot!(operations.iter().map(|op| op.id().hex()).collect_vec(), @r###"
+    [
+        "27f8c802c8378c5c85825365e83928936ae84d7ae3b5bd26d1cd046aa9a2f791dd7b272338d0d2da8a4359523f25daf217f99128a155ba4bc728d279fc3d8f7f",
+        "8a6b19ed474dfad1efa49d64d265f80f74c1d10bf77439900d92d8e6a29fdb64ad1137a92928bfd409096bf84b6fbfb50ebdcc6a28323f9f8e5893548f21b7fb",
+        "65198b538e0f6558d875c49712b0b3570e3a0eb697fd22f5817e39139937b4498e9e9080df1353e116880e36c683f5dddc39d048007ef50da83690a94502bc68",
+        "59da2544953d8d5851e8f64ed5949c8c26f676b87ab84e9fe153bca76912de3753dee8c9cb641f53f57c51a0e876cd43f08c28ca651ad312e5bc09354e9ec40f",
+        "f40d12f62b921bdf96c2d191a4d04845fa26043d131ea1e69eb06fa7a4bbfed6668ab48bed7ec728f7e2c9e675d394b382a332c68399d7f4c446450610479ecf",
+        "2b45a4f90854dd3d4833d998f4fa2e4d4c4eda5212edd3845e8ccb3618d9d538d7a98c173791995898e68d272697ffed1b69838cf839d96cb770856cf499eea8",
+    ]
+    "###);
+
+    // Full id
+    assert_eq!(
+        op_walk::resolve_op_with_repo(&repo, &operations[0].id().hex()).unwrap(),
+        operations[0]
+    );
+    // Short id, odd length
+    assert_eq!(
+        op_walk::resolve_op_with_repo(&repo, &operations[0].id().hex()[..3]).unwrap(),
+        operations[0]
+    );
+    // Short id, even length
+    assert_eq!(
+        op_walk::resolve_op_with_repo(&repo, &operations[1].id().hex()[..2]).unwrap(),
+        operations[1]
+    );
+    // Ambiguous id
+    assert_matches!(
+        op_walk::resolve_op_with_repo(&repo, "2"),
+        Err(OpsetEvaluationError::OpsetResolution(
+            OpsetResolutionError::AmbiguousIdPrefix(_)
+        ))
+    );
+    // Empty id
+    assert_matches!(
+        op_walk::resolve_op_with_repo(&repo, ""),
+        Err(OpsetEvaluationError::OpsetResolution(
+            OpsetResolutionError::InvalidIdPrefix(_)
+        ))
+    );
+    // Unknown id
+    assert_matches!(
+        op_walk::resolve_op_with_repo(&repo, "deadbee"),
+        Err(OpsetEvaluationError::OpsetResolution(
+            OpsetResolutionError::NoSuchOperation(_)
+        ))
+    );
+    // Current op
+    assert_eq!(
+        op_walk::resolve_op_with_repo(&repo, "@").unwrap(),
+        *repo.operation()
+    );
+}
+
+#[test]
+fn test_resolve_op_parents() {
+    // Use monotonic timestamp to stabilize merge order of transactions
+    let settings = testutils::user_settings();
+    let test_repo = TestRepo::init_with_settings(&settings);
+    let mut repo = test_repo.repo;
+
+    let mut operations = Vec::new();
+    for _ in 0..3 {
+        let tx = repo.start_transaction(&settings);
+        repo = tx.commit("test");
+        operations.push(repo.operation().clone());
+    }
+
+    let op2_id_hex = operations[2].id().hex();
+    assert_eq!(
+        op_walk::resolve_op_with_repo(&repo, &format!("{op2_id_hex}-")).unwrap(),
+        operations[1]
+    );
+    assert_eq!(
+        op_walk::resolve_op_with_repo(&repo, &format!("{op2_id_hex}--")).unwrap(),
+        operations[0]
+    );
+    // "{op2_id_hex}---" is the operation to initialize the repo.
+    assert_matches!(
+        op_walk::resolve_op_with_repo(&repo, &format!("{op2_id_hex}----")),
+        Err(OpsetEvaluationError::OpsetResolution(
+            OpsetResolutionError::EmptyOperations(_)
+        ))
+    );
+
+    let tx1 = repo.start_transaction(&settings);
+    let tx2 = repo.start_transaction(&settings);
+    repo = testutils::commit_transactions(&settings, vec![tx1, tx2]);
+    let op5_id_hex = repo.operation().id().hex();
+    assert_matches!(
+        op_walk::resolve_op_with_repo(&repo, &format!("{op5_id_hex}-")),
+        Err(OpsetEvaluationError::OpsetResolution(
+            OpsetResolutionError::MultipleOperations(_)
+        ))
+    );
+}
diff --git a/lib/testutils/src/lib.rs b/lib/testutils/src/lib.rs
index 2995ec2aa..7fd1f1fd0 100644
--- a/lib/testutils/src/lib.rs
+++ b/lib/testutils/src/lib.rs
@@ -131,17 +131,27 @@ impl TestRepo {
     }
 
     pub fn init_with_backend(backend: TestRepoBackend) -> Self {
-        let settings = user_settings();
+        Self::init_with_backend_and_settings(backend, &user_settings())
+    }
+
+    pub fn init_with_settings(settings: &UserSettings) -> Self {
+        Self::init_with_backend_and_settings(TestRepoBackend::Test, settings)
+    }
+
+    pub fn init_with_backend_and_settings(
+        backend: TestRepoBackend,
+        settings: &UserSettings,
+    ) -> Self {
         let temp_dir = new_temp_dir();
 
         let repo_dir = temp_dir.path().join("repo");
         fs::create_dir(&repo_dir).unwrap();
 
         let repo = ReadonlyRepo::init(
-            &settings,
+            settings,
             &repo_dir,
             &move |settings, store_path| backend.init_backend(settings, store_path),
-            Signer::from_settings(&settings).unwrap(),
+            Signer::from_settings(settings).unwrap(),
             ReadonlyRepo::default_op_store_initializer(),
             ReadonlyRepo::default_op_heads_store_initializer(),
             ReadonlyRepo::default_index_store_initializer(),