diff --git a/tests/common/mod.rs b/tests/common/mod.rs
index c0f86472a..79867b24a 100644
--- a/tests/common/mod.rs
+++ b/tests/common/mod.rs
@@ -127,6 +127,7 @@ impl TestEnvironment {
     }
 
     /// Sets up the fake editor to read an edit script from the returned path
+    /// Also sets up the fake editor as a merge tool named "fake-editor"
     pub fn set_up_fake_editor(&mut self) -> PathBuf {
         let editor_path = assert_cmd::cargo::cargo_bin("fake-editor");
         assert!(editor_path.is_file());
@@ -134,6 +135,19 @@ impl TestEnvironment {
         // in it
         let escaped_editor_path = editor_path.to_str().unwrap().replace('\\', r"\\");
         self.add_env_var("EDITOR", &escaped_editor_path);
+        self.add_config(
+            format!(
+                r###"
+                    [ui]
+                    merge-editor = "fake-editor"
+
+                    [merge-tools]
+                    fake-editor.program="{escaped_editor_path}"
+                    fake-editor.merge-args = ["$output"]
+                "###
+            )
+            .as_bytes(),
+        );
         let edit_script = self.env_root().join("edit_script");
         self.add_env_var("EDIT_SCRIPT", edit_script.to_str().unwrap());
         edit_script
@@ -150,9 +164,9 @@ impl TestEnvironment {
         self.add_config(
             format!(
                 r###"
-        [ui]
-        diff-editor = "{}"
-        "###,
+                    [ui]
+                    diff-editor = "{}"
+                "###,
                 escaped_diff_editor_path
             )
             .as_bytes(),
diff --git a/tests/test_resolve_command.rs b/tests/test_resolve_command.rs
new file mode 100644
index 000000000..c0351b27a
--- /dev/null
+++ b/tests/test_resolve_command.rs
@@ -0,0 +1,282 @@
+// Copyright 2022 The Jujutsu Authors
+//
+// Licensed 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
+//
+// https://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.
+
+use std::path::Path;
+
+use crate::common::TestEnvironment;
+
+pub mod common;
+
+fn create_commit(
+    test_env: &TestEnvironment,
+    repo_path: &Path,
+    name: &str,
+    parents: &[&str],
+    files: &[(&str, &str)],
+) {
+    if parents.is_empty() {
+        test_env.jj_cmd_success(repo_path, &["new", "root", "-m", name]);
+    } else {
+        let mut args = vec!["new", "-m", name];
+        args.extend(parents);
+        test_env.jj_cmd_success(repo_path, &args);
+    }
+    for (name, content) in files {
+        std::fs::write(repo_path.join(name), content).unwrap();
+    }
+    test_env.jj_cmd_success(repo_path, &["branch", "create", name]);
+}
+
+fn get_log_output(test_env: &TestEnvironment, repo_path: &Path) -> String {
+    test_env.jj_cmd_success(repo_path, &["log", "-T", "branches"])
+}
+
+#[test]
+fn test_resolution() {
+    let mut test_env = TestEnvironment::default();
+    test_env.jj_cmd_success(test_env.env_root(), &["init", "repo", "--git"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    create_commit(&test_env, &repo_path, "base", &[], &[("file", "base\n")]);
+    create_commit(&test_env, &repo_path, "a", &["base"], &[("file", "a\n")]);
+    create_commit(&test_env, &repo_path, "b", &["base"], &[("file", "b\n")]);
+    create_commit(&test_env, &repo_path, "conflict", &["a", "b"], &[]);
+    // Test the setup
+    insta::assert_snapshot!(get_log_output(&test_env, &repo_path), @r###"
+        @   conflict
+        |\  
+        o | b
+        | o a
+        |/  
+        o base
+        o 
+        "###);
+    insta::assert_snapshot!(
+    std::fs::read_to_string(repo_path.join("file")).unwrap()
+        , @r###"
+            <<<<<<<
+            %%%%%%%
+            -base
+            +a
+            +++++++
+            b
+            >>>>>>>
+            "###);
+
+    let editor_script = test_env.set_up_fake_editor();
+    std::fs::write(
+        editor_script,
+        "expect
+<<<<<<<
+%%%%%%%
+-base
++a
++++++++
+b
+>>>>>>>
+\0write
+resolution
+",
+    )
+    .unwrap();
+    test_env.jj_cmd_success(&repo_path, &["resolve", "file"]);
+    insta::assert_snapshot!(test_env.jj_cmd_success(&repo_path, &["diff", "-r", "conflict"]), 
+    @r###"
+    Resolved conflict in file:
+       1    1: <<<<<<<resolution
+       2     : %%%%%%%
+       3     : -base
+       4     : +a
+       5     : +++++++
+       6     : b
+       7     : >>>>>>>
+    "###);
+}
+
+fn check_resolve_produces_input_file(
+    test_env: &mut TestEnvironment,
+    repo_path: &Path,
+    role: &str,
+    expected_content: &str,
+) {
+    let editor_script = test_env.set_up_fake_editor();
+    std::fs::write(editor_script, format!("expect\n{expected_content}")).unwrap();
+
+    let merge_arg_config = format!(r#"merge-tools.fake-editor.merge-args = ["${role}"]"#);
+    let error = test_env.jj_cmd_failure(
+        repo_path,
+        &["resolve", "--config-toml", &merge_arg_config, "file"],
+    );
+    // This error means that fake-editor exited successfully but did not modify the
+    // output file.
+    insta::assert_snapshot!(error, @r###"
+        Error: Failed to use external tool to resolve: The output file is either unchanged or empty after the editor quit.
+        "###);
+}
+
+#[test]
+fn test_normal_conflict_input_files() {
+    let mut test_env = TestEnvironment::default();
+    test_env.jj_cmd_success(test_env.env_root(), &["init", "repo", "--git"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    create_commit(&test_env, &repo_path, "base", &[], &[("file", "base\n")]);
+    create_commit(&test_env, &repo_path, "a", &["base"], &[("file", "a\n")]);
+    create_commit(&test_env, &repo_path, "b", &["base"], &[("file", "b\n")]);
+    create_commit(&test_env, &repo_path, "conflict", &["a", "b"], &[]);
+    // Test the setup
+    insta::assert_snapshot!(get_log_output(&test_env, &repo_path), @r###"
+        @   conflict
+        |\  
+        o | b
+        | o a
+        |/  
+        o base
+        o 
+        "###);
+    insta::assert_snapshot!(
+    std::fs::read_to_string(repo_path.join("file")).unwrap()
+        , @r###"
+            <<<<<<<
+            %%%%%%%
+            -base
+            +a
+            +++++++
+            b
+            >>>>>>>
+            "###);
+
+    check_resolve_produces_input_file(&mut test_env, &repo_path, "base", "base\n");
+    check_resolve_produces_input_file(&mut test_env, &repo_path, "left", "a\n");
+    check_resolve_produces_input_file(&mut test_env, &repo_path, "right", "b\n");
+}
+
+#[test]
+fn test_baseless_conflict_input_files() {
+    let mut test_env = TestEnvironment::default();
+    test_env.jj_cmd_success(test_env.env_root(), &["init", "repo", "--git"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    create_commit(&test_env, &repo_path, "base", &[], &[]);
+    create_commit(&test_env, &repo_path, "a", &["base"], &[("file", "a\n")]);
+    create_commit(&test_env, &repo_path, "b", &["base"], &[("file", "b\n")]);
+    create_commit(&test_env, &repo_path, "conflict", &["a", "b"], &[]);
+    // Test the setup
+    insta::assert_snapshot!(get_log_output(&test_env, &repo_path), @r###"
+        @   conflict
+        |\  
+        o | b
+        | o a
+        |/  
+        o base
+        o 
+        "###);
+    insta::assert_snapshot!(
+    std::fs::read_to_string(repo_path.join("file")).unwrap()
+        , @r###"
+    <<<<<<<
+    +++++++
+    a
+    +++++++
+    b
+    >>>>>>>
+    "###);
+
+    check_resolve_produces_input_file(&mut test_env, &repo_path, "base", "");
+    check_resolve_produces_input_file(&mut test_env, &repo_path, "left", "a\n");
+    check_resolve_produces_input_file(&mut test_env, &repo_path, "right", "b\n");
+}
+
+#[test]
+fn test_too_many_parents() {
+    let test_env = TestEnvironment::default();
+    test_env.jj_cmd_success(test_env.env_root(), &["init", "repo", "--git"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    create_commit(&test_env, &repo_path, "base", &[], &[("file", "base\n")]);
+    create_commit(&test_env, &repo_path, "a", &["base"], &[("file", "a\n")]);
+    create_commit(&test_env, &repo_path, "b", &["base"], &[("file", "b\n")]);
+    create_commit(&test_env, &repo_path, "c", &["base"], &[("file", "c\n")]);
+    create_commit(&test_env, &repo_path, "conflict", &["a", "b", "c"], &[]);
+
+    let error = test_env.jj_cmd_failure(&repo_path, &["resolve", "file"]);
+    insta::assert_snapshot!(error, @r###"
+    Error: Failed to use external tool to resolve: The conflict at "file" has 2 removes and 3 adds.
+    At most 1 remove and 2 adds are supported.
+    "###);
+}
+
+#[test]
+fn test_edit_delete_conflict_input_files() {
+    let mut test_env = TestEnvironment::default();
+    test_env.jj_cmd_success(test_env.env_root(), &["init", "repo", "--git"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    create_commit(&test_env, &repo_path, "base", &[], &[("file", "base\n")]);
+    create_commit(&test_env, &repo_path, "a", &["base"], &[("file", "a\n")]);
+    create_commit(&test_env, &repo_path, "b", &["base"], &[]);
+    std::fs::remove_file(repo_path.join("file")).unwrap();
+    create_commit(&test_env, &repo_path, "conflict", &["a", "b"], &[]);
+    // Test the setup
+    insta::assert_snapshot!(get_log_output(&test_env, &repo_path), @r###"
+        @   conflict
+        |\  
+        o | b
+        | o a
+        |/  
+        o base
+        o 
+        "###);
+    insta::assert_snapshot!(
+    std::fs::read_to_string(repo_path.join("file")).unwrap()
+        , @r###"
+    <<<<<<<
+    %%%%%%%
+    -base
+    +a
+    >>>>>>>
+    "###);
+
+    check_resolve_produces_input_file(&mut test_env, &repo_path, "base", "base\n");
+    check_resolve_produces_input_file(&mut test_env, &repo_path, "left", "");
+    // Note that `a` ended up in "right" rather than "left". It's unclear if this
+    // can or should be fixed.
+    check_resolve_produces_input_file(&mut test_env, &repo_path, "right", "a\n");
+}
+
+#[test]
+fn test_file_vs_dir() {
+    let test_env = TestEnvironment::default();
+    test_env.jj_cmd_success(test_env.env_root(), &["init", "repo", "--git"]);
+    let repo_path = test_env.env_root().join("repo");
+
+    create_commit(&test_env, &repo_path, "base", &[], &[("file", "base\n")]);
+    create_commit(&test_env, &repo_path, "a", &["base"], &[("file", "a\n")]);
+    create_commit(&test_env, &repo_path, "b", &["base"], &[]);
+    std::fs::remove_file(repo_path.join("file")).unwrap();
+    std::fs::create_dir(repo_path.join("file")).unwrap();
+    // Without a placeholder file, `jj` ignores an empty directory
+    std::fs::write(repo_path.join("file").join("placeholder"), "").unwrap();
+    create_commit(&test_env, &repo_path, "conflict", &["a", "b"], &[]);
+
+    let error = test_env.jj_cmd_failure(&repo_path, &["resolve", "file"]);
+    insta::assert_snapshot!(error, @r###"
+    Error: Failed to use external tool to resolve: Only conflicts that involve normal files (not symlinks, not executable, etc.) are supported. Conflict summary:
+     Conflict:
+      Removing file with id df967b96a579e45a18b8251732d16804b2e56a55
+      Adding file with id 78981922613b2afb6025042ff6bd878ac1994e85
+      Adding tree with id 133bb38fc4e4bf6b551f1f04db7e48f04cac2877
+
+    "###);
+}