diff --git a/src/background/usecases/CommandUseCase.ts b/src/background/usecases/CommandUseCase.ts
index 47208299..73735c5c 100644
--- a/src/background/usecases/CommandUseCase.ts
+++ b/src/background/usecases/CommandUseCase.ts
@@ -70,7 +70,7 @@ export class CommandUseCase {
     // add original command to completed value
     completions.forEach((group) => {
       group.items.forEach((item) => {
-        item.value = name + " " + item.value;
+        item.value = `${name}${force ? "!" : ""} ${item.value}`;
       });
     });
     return completions;
diff --git a/test/background/usecases/CommandUseCase.test.ts b/test/background/usecases/CommandUseCase.test.ts
new file mode 100644
index 00000000..570f5974
--- /dev/null
+++ b/test/background/usecases/CommandUseCase.test.ts
@@ -0,0 +1,150 @@
+import { CommandUseCase } from "../../../src/background/usecases/CommandUseCase";
+import { CommandRegistryImpl } from "../../../src/background/command/CommandRegistry";
+import type { Command } from "../../../src/background/command/types";
+import { describe, beforeAll, test, vi, expect } from "vitest";
+
+const commandA: Command = {
+  names: () => ["a"],
+  fullname: () => "a",
+  description: () => "",
+  getCompletions: () => {
+    throw new Error("not implemented");
+  },
+  exec: () => {
+    throw new Error("not implemented");
+  },
+};
+
+const commandB: Command = {
+  names: () => ["b"],
+  fullname: () => "b",
+  description: () => "",
+  getCompletions: () => {
+    throw new Error("not implemented");
+  },
+  exec: () => {
+    throw new Error("not implemented");
+  },
+};
+
+describe("CommandUseCase", () => {
+  let reg: CommandRegistryImpl;
+
+  beforeAll(() => {
+    reg = new CommandRegistryImpl();
+    reg.register(commandA);
+    reg.register(commandB);
+  });
+
+  const commandAGetCompletion = vi.spyOn(commandA, "getCompletions");
+  const commandAExec = vi.spyOn(commandA, "exec");
+
+  describe("exec", () => {
+    test("executes a command", async () => {
+      const sut = new CommandUseCase(reg);
+      const ctx = { sender: { tab: { id: 1 }, frameId: 1 } as any };
+
+      commandAExec.mockResolvedValue(undefined);
+
+      await sut.exec(ctx, "a 123");
+
+      expect(commandAExec.mock?.lastCall?.[1]).toBe(false);
+      expect(commandAExec.mock?.lastCall?.[2]).toBe("123");
+    });
+
+    test("execute a command with force", async () => {
+      const sut = new CommandUseCase(reg);
+      const ctx = { sender: { tab: { id: 1 }, frameId: 1 } as any };
+
+      commandAExec.mockResolvedValue(undefined);
+
+      await sut.exec(ctx, "a! 123");
+
+      expect(commandAExec.mock?.lastCall?.[1]).toBe(true);
+      expect(commandAExec.mock?.lastCall?.[2]).toBe("123");
+    });
+
+    test("command not found", async () => {
+      const sut = new CommandUseCase(reg);
+      const ctx = { sender: { tab: { id: 1 }, frameId: 1 } as any };
+
+      await expect(() => sut.exec(ctx, "c")).rejects.toThrow(
+        "c command is not defined",
+      );
+    });
+
+    test("empty command", async () => {
+      const sut = new CommandUseCase(reg);
+      const ctx = { sender: { tab: { id: 1 }, frameId: 1 } as any };
+
+      await sut.exec(ctx, "");
+      // no error
+    });
+  });
+
+  describe("getCompletions", () => {
+    test("returns completions of commands", async () => {
+      const sut = new CommandUseCase(reg);
+
+      expect(await sut.getCompletions("")).toEqual([
+        {
+          name: "Console Command",
+          items: [
+            { primary: "a", secondary: "", value: "a" },
+            { primary: "b", secondary: "", value: "b" },
+          ],
+        },
+      ]);
+      expect(await sut.getCompletions("a")).toEqual([
+        {
+          name: "Console Command",
+          items: [{ primary: "a", secondary: "", value: "a" }],
+        },
+      ]);
+    });
+
+    test("returns completions of command arguments", async () => {
+      commandAGetCompletion.mockResolvedValue([
+        {
+          name: "Group",
+          items: [{ value: "item1" }, { value: "item2" }],
+        },
+      ]);
+
+      const sut = new CommandUseCase(reg);
+
+      expect(await sut.getCompletions("a ")).toEqual([
+        {
+          name: "Group",
+          items: [{ value: "a item1" }, { value: "a item2" }],
+        },
+      ]);
+    });
+
+    test("returns completions of command arguments with force", async () => {
+      commandAGetCompletion.mockResolvedValue([
+        {
+          name: "Group",
+          items: [{ value: "item1" }, { value: "item2" }],
+        },
+      ]);
+
+      const sut = new CommandUseCase(reg);
+
+      expect(await sut.getCompletions("a! ")).toEqual([
+        {
+          name: "Group",
+          items: [{ value: "a! item1" }, { value: "a! item2" }],
+        },
+      ]);
+    });
+
+    test("command not found", async () => {
+      const sut = new CommandUseCase(reg);
+
+      await expect(() => sut.getCompletions("c ")).rejects.toThrow(
+        "c command is not defined",
+      );
+    });
+  });
+});