diff --git a/conf.ts b/conf.ts
index 38763e1..ea86d7b 100644
--- a/conf.ts
+++ b/conf.ts
@@ -79,3 +79,13 @@ export function getConfig(): Config {
   };
   return conf;
 }
+
+/** @internal for test */
+function resetConfig(newConf?: Config): void {
+  conf = newConf;
+}
+
+/** @internal */
+export const _internal = {
+  resetConfig,
+};
diff --git a/conf_test.ts b/conf_test.ts
new file mode 100644
index 0000000..88b7da2
--- /dev/null
+++ b/conf_test.ts
@@ -0,0 +1,129 @@
+import {
+  assert,
+  assertEquals,
+  assertObjectMatch,
+  assertThrows,
+} from "jsr:@std/assert@0.225.1";
+import { stub } from "jsr:@std/testing@0.224/mock";
+import { basename, isAbsolute } from "jsr:@std/path@0.224.0";
+import { _internal, getConfig } from "./conf.ts";
+
+const ENV_VARS: Readonly<Record<string, string | undefined>> = {
+  DENOPS_TEST_DENOPS_PATH: "denops.vim",
+  DENOPS_TEST_VIM_EXECUTABLE: undefined,
+  DENOPS_TEST_NVIM_EXECUTABLE: undefined,
+  DENOPS_TEST_VERBOSE: undefined,
+  DENOPS_TEST_CONNECT_TIMEOUT: undefined,
+};
+
+function stubEnvVars(envVars: Readonly<Record<string, string | undefined>>) {
+  return stub(Deno.env, "get", (name) => envVars[name]);
+}
+
+function stubConfModule(): Disposable {
+  const savedConf = getConfig();
+  _internal.resetConfig(undefined);
+  return {
+    [Symbol.dispose]() {
+      _internal.resetConfig(savedConf);
+    },
+  };
+}
+
+Deno.test("getConfig() throws if DENOPS_TEST_DENOPS_PATH env var is not set", () => {
+  using _module = stubConfModule();
+  using _env = stubEnvVars({ ...ENV_VARS, DENOPS_TEST_DENOPS_PATH: undefined });
+  assertThrows(
+    () => {
+      getConfig();
+    },
+    Error,
+    "'DENOPS_TEST_DENOPS_PATH' is required",
+  );
+});
+
+Deno.test("getConfig() returns `{ denopsPath: ... }` with resolved DENOPS_TEST_DENOPS_PATH env var", () => {
+  using _module = stubConfModule();
+  using _env = stubEnvVars({ ...ENV_VARS, DENOPS_TEST_DENOPS_PATH: "foo" });
+  const actual = getConfig();
+  assert(isAbsolute(actual.denopsPath), "`denopsPath` should be absolute path");
+  assertEquals(basename(actual.denopsPath), "foo");
+});
+
+Deno.test("getConfig() returns `{ vimExecutable: 'vim' }` if DENOPS_TEST_VIM_EXECUTABLE env var is not set", () => {
+  using _module = stubConfModule();
+  using _env = stubEnvVars({
+    ...ENV_VARS,
+    DENOPS_TEST_VIM_EXECUTABLE: undefined,
+  });
+  const actual = getConfig();
+  assertObjectMatch(actual, { vimExecutable: "vim" });
+});
+
+Deno.test("getConfig() returns `{ vimExecutable: ... }` with DENOPS_TEST_VIM_EXECUTABLE env var", () => {
+  using _module = stubConfModule();
+  using _env = stubEnvVars({ ...ENV_VARS, DENOPS_TEST_VIM_EXECUTABLE: "foo" });
+  const actual = getConfig();
+  assertObjectMatch(actual, { vimExecutable: "foo" });
+});
+
+Deno.test("getConfig() returns `{ nvimExecutable: 'nvim' }` if DENOPS_TEST_NVIM_EXECUTABLE env var is not set", () => {
+  using _module = stubConfModule();
+  using _env = stubEnvVars({
+    ...ENV_VARS,
+    DENOPS_TEST_NVIM_EXECUTABLE: undefined,
+  });
+  const actual = getConfig();
+  assertObjectMatch(actual, { nvimExecutable: "nvim" });
+});
+
+Deno.test("getConfig() returns `{ nvimExecutable: ... }` with DENOPS_TEST_NVIM_EXECUTABLE env var", () => {
+  using _module = stubConfModule();
+  using _env = stubEnvVars({ ...ENV_VARS, DENOPS_TEST_NVIM_EXECUTABLE: "foo" });
+  const actual = getConfig();
+  assertObjectMatch(actual, { nvimExecutable: "foo" });
+});
+
+Deno.test("getConfig() returns `{ verbose: false }` if DENOPS_TEST_VERBOSE env var is not set", () => {
+  using _module = stubConfModule();
+  using _env = stubEnvVars({ ...ENV_VARS, DENOPS_TEST_VERBOSE: undefined });
+  const actual = getConfig();
+  assertObjectMatch(actual, { verbose: false });
+});
+
+for (
+  const [input, expected] of [
+    ["false", false],
+    ["0", false],
+    ["invalid", false],
+    ["true", true],
+    ["1", true],
+  ] as const
+) {
+  Deno.test(`getConfig() returns \`{ verbose: ${expected} }\` if DENOPS_TEST_VERBOSE env var is '${input}'`, () => {
+    using _module = stubConfModule();
+    using _env = stubEnvVars({ ...ENV_VARS, DENOPS_TEST_VERBOSE: input });
+    const actual = getConfig();
+    assertObjectMatch(actual, { verbose: expected });
+  });
+}
+
+for (
+  const [input, expected] of [
+    ["123", 123],
+    ["123.456", 123],
+    ["0", undefined],
+    ["-123", undefined],
+    ["string", undefined],
+  ] as const
+) {
+  Deno.test(`getConfig() returns \`{ connectTimeout: ${expected} }\` if DENOPS_TEST_CONNECT_TIMEOUT env var is '${input}'`, () => {
+    using _module = stubConfModule();
+    using _env = stubEnvVars({
+      ...ENV_VARS,
+      DENOPS_TEST_CONNECT_TIMEOUT: input,
+    });
+    const actual = getConfig();
+    assertObjectMatch(actual, { connectTimeout: expected });
+  });
+}
diff --git a/with_test.ts b/with_test.ts
index 88f8b5d..638873c 100644
--- a/with_test.ts
+++ b/with_test.ts
@@ -1,5 +1,10 @@
-import { assert, assertFalse, assertRejects } from "jsr:@std/assert@0.225.1";
-import { assertSpyCalls, spy } from "jsr:@std/testing@0.224.0/mock";
+import {
+  assert,
+  assertEquals,
+  assertFalse,
+  assertRejects,
+} from "jsr:@std/assert@0.225.1";
+import { assertSpyCalls, spy, stub } from "jsr:@std/testing@0.224.0/mock";
 import type { Denops } from "jsr:@denops/core@6.0.6";
 import { withDenops } from "./with.ts";
 
@@ -20,6 +25,78 @@ Deno.test("test(mode:nvim) start nvim to test denops features", async () => {
 });
 
 for (const mode of ["vim", "nvim"] as const) {
+  Deno.test(`test(mode:${mode}) outputs ${mode} messages if 'verbose' option is true`, async () => {
+    using s = stub(console, "error");
+    await withDenops("vim", async (denops: Denops) => {
+      await denops.cmd("echomsg 'foobar'");
+    }, { verbose: true });
+    // NOTE: Maybe some other values are included, so find target with `Array.some`.
+    // NOTE: Maybe "\r" or "\n" is prepend or postpend, so use `String.trim`.
+    assert(s.calls.some((c) => c.args[0].trim() === "foobar"));
+  });
+
+  Deno.test(`test(mode:${mode}) should be able to call Denops#redraw()`, async () => {
+    await withDenops("vim", async (denops: Denops) => {
+      await denops.redraw();
+      await denops.redraw(true);
+      // FIXME: assert redraw is correctly called.
+    });
+  });
+
+  Deno.test(`test(mode:${mode}) should be able to call Denops#call()`, async () => {
+    await withDenops("vim", async (denops: Denops) => {
+      await denops.call("execute", [`let g:with_test__${mode}__call = 'foo'`]);
+      assertEquals(await denops.eval(`g:with_test__${mode}__call`), "foo");
+    });
+  });
+
+  Deno.test(`test(mode:${mode}) should be able to call Denops#batch()`, async () => {
+    await withDenops("vim", async (denops: Denops) => {
+      await denops.batch(
+        ["execute", [`let g:with_test__${mode}__batch_1 = 'foo'`]],
+        ["execute", [`let g:with_test__${mode}__batch_2 = 'bar'`]],
+      );
+      assertEquals(await denops.eval(`g:with_test__${mode}__batch_1`), "foo");
+      assertEquals(await denops.eval(`g:with_test__${mode}__batch_2`), "bar");
+    });
+  });
+
+  Deno.test(`test(mode:${mode}) should be able to call Denops#cmd()`, async () => {
+    await withDenops("vim", async (denops: Denops) => {
+      await denops.cmd(`let g:with_test__${mode}__cmd = 'foo'`);
+      assertEquals(await denops.eval(`g:with_test__${mode}__cmd`), "foo");
+    });
+  });
+
+  Deno.test(`test(mode:${mode}) should be able to call Denops#eval()`, async () => {
+    await withDenops("vim", async (denops: Denops) => {
+      await denops.eval(`execute('let g:with_test__${mode}__eval = "foo"')`);
+      assertEquals(await denops.eval(`g:with_test__${mode}__eval`), "foo");
+    });
+  });
+
+  Deno.test(`test(mode:${mode}) should be able to call Denops#dispatch()`, async () => {
+    const api = spy(() => Promise.resolve());
+    await withDenops("vim", async (denops: Denops) => {
+      denops.dispatcher = {
+        foo: api,
+      };
+      await denops.dispatch(denops.name, "foo", [123, "bar"]);
+      assertSpyCalls(api, 1);
+    });
+  });
+
+  Deno.test(`test(mode:${mode}) calls plugin dispatcher from ${mode}`, async () => {
+    const api = spy(() => Promise.resolve());
+    await withDenops("vim", async (denops: Denops) => {
+      denops.dispatcher = {
+        foo: api,
+      };
+      await denops.call("denops#notify", denops.name, "foo", [123, "bar"]);
+      assertSpyCalls(api, 1);
+    });
+  });
+
   Deno.test(`test(mode:${mode}) rejects if process aborted`, async () => {
     const fn = spy(() => {});
     await assertRejects(