diff --git a/expect/_assertions_test.ts b/expect/_assertions_test.ts
index f59764cbeb5a..6e33fe4abc44 100644
--- a/expect/_assertions_test.ts
+++ b/expect/_assertions_test.ts
@@ -1,64 +1,180 @@
 // Copyright 2018-2025 the Deno authors. MIT license.
 
-import { describe, it, test } from "@std/testing/bdd";
-import { expect } from "./expect.ts";
-
-Deno.test("expect.hasAssertions() API", () => {
-  describe("describe suite", () => {
-    // FIXME(eryue0220): This test should through `toThrowErrorMatchingSnapshot`
-    it("should throw an error", () => {
-      expect.hasAssertions();
-    });
+import * as path from "@std/path";
+import { assertStringIncludes } from "@std/assert";
+import { stripAnsiCode } from "@std/internal/styles";
 
-    it("should pass", () => {
-      expect.hasAssertions();
-      expect("a").toEqual("a");
-    });
-  });
-
-  it("it() suite should pass", () => {
-    expect.hasAssertions();
-    expect("a").toEqual("a");
+Deno.test("expect.hasAssertions() API", async () => {
+  const tempDirPath = await Deno.makeTempDir({
+    prefix: "deno_std_has_assertions_",
   });
+  try {
+    const tempFilePath = path.join(tempDirPath, "has_assertions_test.ts");
+    await Deno.writeTextFile(
+      tempFilePath,
+      `import { describe, it, test } from "@std/testing/bdd";
+import { expect } from "@std/expect";
 
-  // FIXME(eryue0220): This test should through `toThrowErrorMatchingSnapshot`
-  test("test suite should throw an error", () => {
+describe("describe suite", () => {
+  it("describe should throw an error", () => {
     expect.hasAssertions();
   });
 
-  test("test suite should pass", () => {
+  it("describe should pass", () => {
     expect.hasAssertions();
     expect("a").toEqual("a");
   });
 });
 
-Deno.test("expect.assertions() API", () => {
-  test("should pass", () => {
-    expect.assertions(2);
-    expect("a").not.toBe("b");
-    expect("a").toBe("a");
-  });
+it("it() suite should throw an error", () => {
+  expect.hasAssertions();
+});
 
-  // FIXME(eryue0220): This test should through `toThrowErrorMatchingSnapshot`
-  test("should throw error", () => {
-    expect.assertions(1);
-    expect("a").not.toBe("b");
-    expect("a").toBe("a");
-  });
+it("it() suite should pass", () => {
+  expect.hasAssertions();
+  expect("a").toEqual("a");
+});
 
-  it("redeclare different assertion count", () => {
-    expect.assertions(3);
-    expect("a").not.toBe("b");
-    expect("a").toBe("a");
-    expect.assertions(2);
-  });
+test("test suite should throw an error", () => {
+  expect.hasAssertions();
+});
+
+test("test suite should pass", () => {
+  expect.hasAssertions();
+  expect("a").toEqual("a");
+});
+`,
+    );
+
+    const command = new Deno.Command(Deno.execPath(), {
+      args: ["test", "--no-lock", tempDirPath],
+    });
+    const { stdout } = await command.output();
+    const errorMessage = stripAnsiCode(new TextDecoder().decode(stdout));
+
+    assertStringIncludes(
+      errorMessage,
+      "describe should throw an error ... FAILED",
+    );
+    assertStringIncludes(errorMessage, "describe should pass ... ok");
+    assertStringIncludes(
+      errorMessage,
+      "it() suite should throw an error ... FAILED",
+    );
+    assertStringIncludes(errorMessage, "it() suite should pass ... ok");
+    assertStringIncludes(
+      errorMessage,
+      "test suite should throw an error ... FAILED",
+    );
+    assertStringIncludes(errorMessage, "test suite should pass ... ok");
 
-  test("expect no assertions", () => {
-    expect.assertions(0);
+    assertStringIncludes(
+      errorMessage,
+      "error: AssertionError: Expected at least one assertion to be called but received none",
+    );
+  } finally {
+    await Deno.remove(tempDirPath, { recursive: true });
+  }
+});
+
+Deno.test("expect.assertions() API", async () => {
+  const tempDirPath = await Deno.makeTempDir({
+    prefix: "deno_std_has_assertions_",
   });
+  try {
+    const tempFilePath = path.join(tempDirPath, "has_assertions_test.ts");
+    await Deno.writeTextFile(
+      tempFilePath,
+      `import { describe, it, test } from "@std/testing/bdd";
+import { expect } from "@std/expect";
 
-  // FIXME(eryue0220): This test should through `toThrowErrorMatchingSnapshot`
-  it("should throw an error", () => {
-    expect.assertions(2);
+test("should pass", () => {
+  expect.assertions(2);
+  expect("a").not.toBe("b");
+  expect("a").toBe("a");
+});
+
+test("should throw error", () => {
+  expect.assertions(1);
+  expect("a").not.toBe("b");
+  expect("a").toBe("a");
+});
+
+it("redeclare different assertion count", () => {
+  expect.assertions(3);
+  expect("a").not.toBe("b");
+  expect("a").toBe("a");
+  expect.assertions(2);
+});
+
+test("expect no assertions", () => {
+  expect.assertions(0);
+});
+
+it("should throw an error", () => {
+  expect.assertions(2);
+});
+`,
+    );
+
+    const command = new Deno.Command(Deno.execPath(), {
+      args: ["test", "--no-lock", tempDirPath],
+    });
+    const { stdout } = await command.output();
+    const errorMessage = stripAnsiCode(new TextDecoder().decode(stdout));
+
+    assertStringIncludes(errorMessage, "should pass ... ok");
+    assertStringIncludes(errorMessage, "should throw error ... FAILED");
+    assertStringIncludes(
+      errorMessage,
+      "redeclare different assertion count ... ok",
+    );
+    assertStringIncludes(errorMessage, "expect no assertions ... ok");
+    assertStringIncludes(errorMessage, "should throw an error ... FAILED");
+
+    assertStringIncludes(
+      errorMessage,
+      "error: AssertionError: Expected exactly 1 assertion to be called, but received 2",
+    );
+    assertStringIncludes(
+      errorMessage,
+      "error: AssertionError: Expected exactly 2 assertions to be called, but received 0",
+    );
+  } finally {
+    await Deno.remove(tempDirPath, { recursive: true });
+  }
+});
+
+Deno.test("expect assertions reset after errored tests", async () => {
+  const tempDirPath = await Deno.makeTempDir({
+    prefix: "deno_std_assertions_reset_",
   });
+  try {
+    const tempFilePath = path.join(tempDirPath, "assertion_reset_test.ts");
+    await Deno.writeTextFile(
+      tempFilePath,
+      `import { it } from "@std/testing/bdd";
+import { expect } from "@std/expect";
+it("should fail", () => {
+  expect.assertions(2);
+  expect(1).toBe(1);
+});
+it("should pass", () => {
+  expect.assertions(0);
+});
+`,
+    );
+
+    const command = new Deno.Command(Deno.execPath(), {
+      args: ["test", "--no-lock", tempDirPath],
+    });
+    const { stdout } = await command.output();
+    const errorMessage = stripAnsiCode(new TextDecoder().decode(stdout));
+
+    assertStringIncludes(errorMessage, "should fail ... FAILED");
+    // Previously "should fail" failing caused "should pass" to fail
+    assertStringIncludes(errorMessage, "should pass ... ok");
+  } finally {
+    await Deno.remove(tempDirPath, { recursive: true });
+  }
 });
diff --git a/internal/assertion_state.ts b/internal/assertion_state.ts
index 6a1b79ab6632..3e29925a4b31 100644
--- a/internal/assertion_state.ts
+++ b/internal/assertion_state.ts
@@ -26,6 +26,20 @@ export class AssertionState {
       assertionTriggered: false,
       assertionTriggeredCount: 0,
     };
+
+    // If any checks were registered, after the test suite runs the checks,
+    // `resetAssertionState` should also have been called. If it was not,
+    // then the test suite did not run the checks.
+    globalThis.addEventListener("unload", () => {
+      if (
+        this.#state.assertionCheck ||
+        this.#state.assertionCount !== undefined
+      ) {
+        throw new Error(
+          "AssertionCounter was not cleaned up: If tests are not otherwise failing, ensure `expect.hasAssertion` and `expect.assertions` are only run in bdd tests",
+        );
+      }
+    });
   }
 
   /**
diff --git a/internal/assertion_state_test.ts b/internal/assertion_state_test.ts
index ad3148cddd1f..e3453f83916d 100644
--- a/internal/assertion_state_test.ts
+++ b/internal/assertion_state_test.ts
@@ -1,28 +1,56 @@
 // Copyright 2018-2025 the Deno authors. MIT license.
 
-import { assertEquals } from "@std/assert";
+import { assertEquals, assertStringIncludes } from "@std/assert";
 import { AssertionState } from "./assertion_state.ts";
+import { stripAnsiCode } from "./styles.ts";
 
 Deno.test("AssertionState checkAssertionErrorState pass", () => {
   const assertionState = new AssertionState();
-  assertionState.setAssertionTriggered(true);
-
-  assertEquals(assertionState.checkAssertionErrorState(), false);
+  try {
+    assertionState.setAssertionTriggered(true);
+    assertEquals(assertionState.checkAssertionErrorState(), false);
+  } finally {
+    assertionState.resetAssertionState();
+  }
 });
 
 Deno.test("AssertionState checkAssertionErrorState pass", () => {
   const assertionState = new AssertionState();
-  assertionState.setAssertionTriggered(true);
+  try {
+    assertionState.setAssertionTriggered(true);
 
-  assertEquals(assertionState.checkAssertionErrorState(), false);
+    assertEquals(assertionState.checkAssertionErrorState(), false);
 
-  assertionState.setAssertionCheck(true);
-  assertEquals(assertionState.checkAssertionErrorState(), false);
+    assertionState.setAssertionCheck(true);
+    assertEquals(assertionState.checkAssertionErrorState(), false);
+  } finally {
+    assertionState.resetAssertionState();
+  }
 });
 
 Deno.test("AssertionState checkAssertionErrorState fail", () => {
   const assertionState = new AssertionState();
-  assertionState.setAssertionCheck(true);
+  try {
+    assertionState.setAssertionCheck(true);
+    assertEquals(assertionState.checkAssertionErrorState(), true);
+  } finally {
+    assertionState.resetAssertionState();
+  }
+});
 
-  assertEquals(assertionState.checkAssertionErrorState(), true);
+Deno.test("AssertionState throws if not cleaned up", async () => {
+  const command = new Deno.Command(Deno.execPath(), {
+    args: [
+      "eval",
+      `
+        import { AssertionState } from "@std/internal/assertion-state";
+        const assertionState = new AssertionState();
+        assertionState.setAssertionCount(0);
+      `,
+    ],
+  });
+  const { stderr } = await command.output();
+  const errorMessage = stripAnsiCode(new TextDecoder().decode(stderr));
+  // TODO(WWRS): Test for the expected message when Deno displays it instead of "Uncaught null"
+  assertStringIncludes(errorMessage, "error: Uncaught");
 });
diff --git a/testing/_test_suite.ts b/testing/_test_suite.ts
index 055bdd428740..b2cf1b60b926 100644
--- a/testing/_test_suite.ts
+++ b/testing/_test_suite.ts
@@ -429,19 +429,23 @@ export class TestSuiteInternal<T> implements TestSuite<T> {
       await fn.call(context, t);
     }
 
-    if (assertionState.checkAssertionErrorState()) {
-      throw new AssertionError(
-        "Expected at least one assertion to be called but received none",
-      );
-    }
+    try {
+      if (assertionState.checkAssertionErrorState()) {
+        throw new AssertionError(
+          "Expected at least one assertion to be called but received none",
+        );
+      }
 
-    if (assertionState.checkAssertionCountSatisfied()) {
-      throw new AssertionError(
-        `Expected at least ${assertionState.assertionCount} assertion to be called, ` +
-          `but received ${assertionState.assertionTriggeredCount}`,
-      );
+      if (assertionState.checkAssertionCountSatisfied()) {
+        throw new AssertionError(
+          `Expected exactly ${assertionState.assertionCount} ${
+            assertionState.assertionCount === 1 ? "assertion" : "assertions"
+          } to be called, ` +
+            `but received ${assertionState.assertionTriggeredCount}`,
+        );
+      }
+    } finally {
+      assertionState.resetAssertionState();
     }
-
-    assertionState.resetAssertionState();
   }
 }
diff --git a/testing/bdd.ts b/testing/bdd.ts
index f14efbd65832..3f23edc294ec 100644
--- a/testing/bdd.ts
+++ b/testing/bdd.ts
@@ -600,20 +600,24 @@ export function it<T>(...args: ItArgs<T>) {
           TestSuiteInternal.runningCount--;
         }
 
-        if (assertionState.checkAssertionErrorState()) {
-          throw new AssertionError(
-            "Expected at least one assertion to be called but received none",
-          );
-        }
+        try {
+          if (assertionState.checkAssertionErrorState()) {
+            throw new AssertionError(
+              "Expected at least one assertion to be called but received none",
+            );
+          }
 
-        if (assertionState.checkAssertionCountSatisfied()) {
-          throw new AssertionError(
-            `Expected at least ${assertionState.assertionCount} assertion to be called, ` +
-              `but received ${assertionState.assertionTriggeredCount}`,
-          );
+          if (assertionState.checkAssertionCountSatisfied()) {
+            throw new AssertionError(
+              `Expected exactly ${assertionState.assertionCount} ${
+                assertionState.assertionCount === 1 ? "assertion" : "assertions"
+              } to be called, ` +
+                `but received ${assertionState.assertionTriggeredCount}`,
+            );
+          }
+        } finally {
+          assertionState.resetAssertionState();
         }
-
-        assertionState.resetAssertionState();
       },
     };
     if (ignore !== undefined) {