diff --git a/testing/asserts.ts b/testing/asserts.ts
index 6431a11a5b..33d6073eaf 100644
--- a/testing/asserts.ts
+++ b/testing/asserts.ts
@@ -6,6 +6,13 @@ interface Constructor {
   new (...args: any[]): any;
 }
 
+export class AssertionError extends Error {
+  constructor(message: string) {
+    super(message);
+    this.name = "AssertionError";
+  }
+}
+
 export function equal(c: unknown, d: unknown): boolean {
   const seen = new Map();
   return (function compare(a: unknown, b: unknown) {
@@ -36,7 +43,7 @@ export function equal(c: unknown, d: unknown): boolean {
 /** Make an assertion, if not `true`, then throw. */
 export function assert(expr: boolean, msg = ""): void {
   if (!expr) {
-    throw new Error(msg);
+    throw new AssertionError(msg);
   }
 }
 
@@ -85,7 +92,7 @@ export function assertNotEquals(
   if (!msg) {
     msg = `actual: ${actualString} expected: ${expectedString}`;
   }
-  throw new Error(msg);
+  throw new AssertionError(msg);
 }
 
 /**
@@ -119,7 +126,7 @@ export function assertStrictEq(
     if (!msg) {
       msg = `actual: ${actualString} expected: ${expectedString}`;
     }
-    throw new Error(msg);
+    throw new AssertionError(msg);
   }
 }
 
@@ -142,7 +149,7 @@ export function assertStrContains(
     if (!msg) {
       msg = `actual: "${actual}" expected to contains: "${expected}"`;
     }
-    throw new Error(msg);
+    throw new AssertionError(msg);
   }
 }
 
@@ -182,7 +189,7 @@ export function assertArrayContains(
     msg += "\n";
     msg += `missing: ${missing}`;
   }
-  throw new Error(msg);
+  throw new AssertionError(msg);
 }
 
 /**
@@ -204,7 +211,7 @@ export function assertMatch(
     if (!msg) {
       msg = `actual: "${actual}" expected to match: "${expected}"`;
     }
-    throw new Error(msg);
+    throw new AssertionError(msg);
   }
 }
 
@@ -234,21 +241,19 @@ export function assertThrows(
       msg = `Expected error to be instance of "${ErrorClass.name}"${
         msg ? `: ${msg}` : "."
       }`;
-      throw new Error(msg);
+      throw new AssertionError(msg);
     }
-    if (msgIncludes) {
-      if (!e.message.includes(msgIncludes)) {
-        msg = `Expected error message to include "${msgIncludes}", but got "${
-          e.message
-        }"${msg ? `: ${msg}` : "."}`;
-        throw new Error(msg);
-      }
+    if (msgIncludes && !e.message.includes(msgIncludes)) {
+      msg = `Expected error message to include "${msgIncludes}", but got "${
+        e.message
+      }"${msg ? `: ${msg}` : "."}`;
+      throw new AssertionError(msg);
     }
     doesThrow = true;
   }
   if (!doesThrow) {
     msg = `Expected function to throw${msg ? `: ${msg}` : "."}`;
-    throw new Error(msg);
+    throw new AssertionError(msg);
   }
 }
 
@@ -266,30 +271,28 @@ export async function assertThrowsAsync(
       msg = `Expected error to be instance of "${ErrorClass.name}"${
         msg ? `: ${msg}` : "."
       }`;
-      throw new Error(msg);
+      throw new AssertionError(msg);
     }
-    if (msgIncludes) {
-      if (!e.message.includes(msgIncludes)) {
-        msg = `Expected error message to include "${msgIncludes}", but got "${
-          e.message
-        }"${msg ? `: ${msg}` : "."}`;
-        throw new Error(msg);
-      }
+    if (msgIncludes && !e.message.includes(msgIncludes)) {
+      msg = `Expected error message to include "${msgIncludes}", but got "${
+        e.message
+      }"${msg ? `: ${msg}` : "."}`;
+      throw new AssertionError(msg);
     }
     doesThrow = true;
   }
   if (!doesThrow) {
     msg = `Expected function to throw${msg ? `: ${msg}` : "."}`;
-    throw new Error(msg);
+    throw new AssertionError(msg);
   }
 }
 
 /** Use this to stub out methods that will throw when invoked. */
 export function unimplemented(msg?: string): never {
-  throw new Error(msg || "unimplemented");
+  throw new AssertionError(msg || "unimplemented");
 }
 
 /** Use this to assert unreachable code. */
 export function unreachable(): never {
-  throw new Error("unreachable");
+  throw new AssertionError("unreachable");
 }
diff --git a/testing/asserts_test.ts b/testing/asserts_test.ts
index ccec2af090..6f82d41697 100644
--- a/testing/asserts_test.ts
+++ b/testing/asserts_test.ts
@@ -2,20 +2,19 @@
 
 import {
   assert,
-  equal,
   assertNotEquals,
   assertStrContains,
   assertArrayContains,
   assertMatch,
   assertEquals,
+  assertThrows,
+  AssertionError,
+  equal,
+  fail,
   unimplemented,
   unreachable
 } from "./asserts.ts";
 import { test } from "./mod.ts";
-// import { assertEquals as prettyAssertEqual } from "./pretty.ts";
-// import "./format_test.ts";
-// import "./diff_test.ts";
-// import "./pretty_test.ts";
 
 test(function testingEqual() {
   assert(equal("world", "world"));
@@ -49,6 +48,7 @@ test(function testingNotEquals() {
     assertNotEquals("Raptor", "Raptor");
     didThrow = false;
   } catch (e) {
+    assert(e instanceof AssertionError);
     didThrow = true;
   }
   assertEquals(didThrow, true);
@@ -63,6 +63,7 @@ test(function testingAssertStringContains() {
     assertStrContains("Denosaurus", "Raptor");
     didThrow = false;
   } catch (e) {
+    assert(e instanceof AssertionError);
     didThrow = true;
   }
   assertEquals(didThrow, true);
@@ -78,6 +79,7 @@ test(function testingArrayContains() {
     assertArrayContains(fixtureObject, [{ deno: "node" }]);
     didThrow = false;
   } catch (e) {
+    assert(e instanceof AssertionError);
     didThrow = true;
   }
   assertEquals(didThrow, true);
@@ -92,6 +94,7 @@ test(function testingAssertStringContainsThrow() {
       e.message ===
         `actual: "Denosaurus from Jurassic" expected to contains: "Raptor"`
     );
+    assert(e instanceof AssertionError);
     didThrow = true;
   }
   assert(didThrow);
@@ -110,6 +113,7 @@ test(function testingAssertStringMatchingThrows() {
       e.message ===
         `actual: "Denosaurus from Jurassic" expected to match: "/Raptor/"`
     );
+    assert(e instanceof AssertionError);
     didThrow = true;
   }
   assert(didThrow);
@@ -121,6 +125,7 @@ test(function testingAssertsUnimplemented() {
     unimplemented();
   } catch (e) {
     assert(e.message === "unimplemented");
+    assert(e instanceof AssertionError);
     didThrow = true;
   }
   assert(didThrow);
@@ -132,7 +137,19 @@ test(function testingAssertsUnreachable() {
     unreachable();
   } catch (e) {
     assert(e.message === "unreachable");
+    assert(e instanceof AssertionError);
     didThrow = true;
   }
   assert(didThrow);
 });
+
+test(function testingAssertFail() {
+  assertThrows(fail, AssertionError, "Failed assertion.");
+  assertThrows(
+    () => {
+      fail("foo");
+    },
+    AssertionError,
+    "Failed assertion: foo"
+  );
+});
diff --git a/testing/test.ts b/testing/test.ts
index 7f904346c3..367e280228 100644
--- a/testing/test.ts
+++ b/testing/test.ts
@@ -5,25 +5,13 @@ import {
   assertEquals,
   assertStrictEq,
   assertThrows,
-  assertThrowsAsync,
-  fail
+  assertThrowsAsync
 } from "../testing/asserts.ts";
 import "./format_test.ts";
 import "./diff_test.ts";
 import "./pretty_test.ts";
 import "./asserts_test.ts";
 
-test(function testingAssertFail() {
-  assertThrows(fail, Error, "Failed assertion.");
-  assertThrows(
-    () => {
-      fail("foo");
-    },
-    Error,
-    "Failed assertion: foo"
-  );
-});
-
 test(function testingAssertEqualActualUncoercable() {
   let didThrow = false;
   const a = Object.create(null);