fix(std/testing): assertThrows gracefully fails if non-Error thrown (#6330)

std/testing/asserts.ts

@@ -322,7 +322,8 @@ export function fail(msg?: string): void {
   assert(false, `Failed assertion${msg ? `: ${msg}` : "."}`);
 }
 
-/** Executes a function, expecting it to throw.  If it does not, then it
+/**
+ * Executes a function, expecting it to throw.  If it does not, then it
  * throws.  An error class and a string that should be included in the
  * error message can also be asserted.
  */
@@ -337,6 +338,9 @@ export function assertThrows<T = void>(
   try {
     fn();
   } catch (e) {
+    if (e instanceof Error === false) {
+      throw new AssertionError("A non-Error object was thrown.");
+    }
     if (ErrorClass && !(Object.getPrototypeOf(e) === ErrorClass.prototype)) {
       msg = `Expected error to be instance of "${ErrorClass.name}", but was "${
         e.constructor.name
@@ -362,6 +366,11 @@ export function assertThrows<T = void>(
   return error;
 }
 
+/**
+ * Executes a function which returns a promise, expecting it to throw or reject.
+ * If it does not, then it throws.  An error class and a string that should be
+ * included in the error message can also be asserted.
+ */
 export async function assertThrowsAsync<T = void>(
   fn: () => Promise<T>,
   ErrorClass?: Constructor,
@@ -373,6 +382,9 @@ export async function assertThrowsAsync<T = void>(
   try {
     await fn();
   } catch (e) {
+    if (e instanceof Error === false) {
+      throw new AssertionError("A non-Error object was thrown or rejected.");
+    }
     if (ErrorClass && !(Object.getPrototypeOf(e) === ErrorClass.prototype)) {
       msg = `Expected error to be instance of "${ErrorClass.name}", but got "${
         e.name

std/testing/asserts_test.ts

@@ -409,3 +409,86 @@ Deno.test({
     );
   },
 });
+
+Deno.test("Assert Throws Non-Error Fail", () => {
+  assertThrows(
+    () => {
+      assertThrows(
+        () => {
+          throw "Panic!";
+        },
+        String,
+        "Panic!"
+      );
+    },
+    AssertionError,
+    "A non-Error object was thrown."
+  );
+
+  assertThrows(
+    () => {
+      assertThrows(() => {
+        throw null;
+      });
+    },
+    AssertionError,
+    "A non-Error object was thrown."
+  );
+
+  assertThrows(
+    () => {
+      assertThrows(() => {
+        throw undefined;
+      });
+    },
+    AssertionError,
+    "A non-Error object was thrown."
+  );
+});
+
+Deno.test("Assert Throws Async Non-Error Fail", () => {
+  assertThrowsAsync(
+    () => {
+      return assertThrowsAsync(
+        () => {
+          return Promise.reject("Panic!");
+        },
+        String,
+        "Panic!"
+      );
+    },
+    AssertionError,
+    "A non-Error object was thrown or rejected."
+  );
+
+  assertThrowsAsync(
+    () => {
+      return assertThrowsAsync(() => {
+        return Promise.reject(null);
+      });
+    },
+    AssertionError,
+    "A non-Error object was thrown or rejected."
+  );
+
+  assertThrowsAsync(
+    () => {
+      return assertThrowsAsync(() => {
+        return Promise.reject(undefined);
+      });
+    },
+    AssertionError,
+    "A non-Error object was thrown or rejected."
+  );
+
+  assertThrowsAsync(
+    () => {
+      return assertThrowsAsync(() => {
+        throw undefined;
+        return Promise.resolve("Ok!");
+      });
+    },
+    AssertionError,
+    "A non-Error object was thrown or rejected."
+  );
+});