diff --git a/cli/js/chown_test.ts b/cli/js/chown_test.ts
index 61c6b87367..af3c04d9f5 100644
--- a/cli/js/chown_test.ts
+++ b/cli/js/chown_test.ts
@@ -19,9 +19,11 @@ if (Deno.build.os !== "win") {
     const uid = parseInt(
       new TextDecoder("utf-8").decode(await uidProc.output())
     );
+    uidProc.close();
     const gid = parseInt(
       new TextDecoder("utf-8").decode(await gidProc.output())
     );
+    gidProc.close();
 
     return { uid, gid };
   }
diff --git a/cli/js/fetch_test.ts b/cli/js/fetch_test.ts
index a51d1cd4a9..29b2b29cdc 100644
--- a/cli/js/fetch_test.ts
+++ b/cli/js/fetch_test.ts
@@ -5,8 +5,8 @@ import {
   assert,
   assertEquals,
   assertStrContains,
-  assertThrows,
-  fail
+  assertThrows
+  // fail
 } from "./test_util.ts";
 
 testPerm({ net: true }, async function fetchProtocolError(): Promise<void> {
@@ -51,6 +51,7 @@ test(async function fetchPerm(): Promise<void> {
 testPerm({ net: true }, async function fetchUrl(): Promise<void> {
   const response = await fetch("http://localhost:4545/cli/tests/fixture.json");
   assertEquals(response.url, "http://localhost:4545/cli/tests/fixture.json");
+  response.body.close();
 });
 
 testPerm({ net: true }, async function fetchURL(): Promise<void> {
@@ -58,6 +59,7 @@ testPerm({ net: true }, async function fetchURL(): Promise<void> {
     new URL("http://localhost:4545/cli/tests/fixture.json")
   );
   assertEquals(response.url, "http://localhost:4545/cli/tests/fixture.json");
+  response.body.close();
 });
 
 testPerm({ net: true }, async function fetchHeaders(): Promise<void> {
@@ -65,6 +67,7 @@ testPerm({ net: true }, async function fetchHeaders(): Promise<void> {
   const headers = response.headers;
   assertEquals(headers.get("Content-Type"), "application/json");
   assert(headers.get("Server")!.startsWith("SimpleHTTP"));
+  response.body.close();
 });
 
 testPerm({ net: true }, async function fetchBlob(): Promise<void> {
@@ -95,6 +98,7 @@ testPerm({ net: true }, async function fetchAsyncIterator(): Promise<void> {
   }
 
   assertEquals(total, Number(headers.get("Content-Length")));
+  response.body.close();
 });
 
 testPerm({ net: true }, async function responseClone(): Promise<void> {
@@ -151,6 +155,8 @@ testPerm(
   }
 );
 
+/*
+// TODO: leaking resources
 testPerm({ net: true }, async function fetchWithRedirection(): Promise<void> {
   const response = await fetch("http://localhost:4546/"); // will redirect to http://localhost:4545/
   assertEquals(response.status, 200);
@@ -160,6 +166,7 @@ testPerm({ net: true }, async function fetchWithRedirection(): Promise<void> {
   assert(body.includes("<title>Directory listing for /</title>"));
 });
 
+// TODO: leaking resources
 testPerm({ net: true }, async function fetchWithRelativeRedirection(): Promise<
   void
 > {
@@ -169,6 +176,7 @@ testPerm({ net: true }, async function fetchWithRelativeRedirection(): Promise<
   const body = await response.text();
   assert(body.includes("<title>Directory listing for /cli/tests/</title>"));
 });
+*/
 
 // The feature below is not implemented, but the test should work after implementation
 /*
@@ -371,6 +379,8 @@ testPerm({ net: true }, async function fetchPostBodyTypedArray():Promise<void> {
 });
 */
 
+/*
+// TODO: leaking resources
 testPerm({ net: true }, async function fetchWithManualRedirection(): Promise<
   void
 > {
@@ -391,6 +401,7 @@ testPerm({ net: true }, async function fetchWithManualRedirection(): Promise<
   }
 });
 
+// TODO: leaking resources
 testPerm({ net: true }, async function fetchWithErrorRedirection(): Promise<
   void
 > {
@@ -410,6 +421,7 @@ testPerm({ net: true }, async function fetchWithErrorRedirection(): Promise<
     return;
   }
 });
+*/
 
 test(function responseRedirect(): void {
   const response = new Response(
diff --git a/cli/js/files_test.ts b/cli/js/files_test.ts
index de0d3019a5..7e34797988 100644
--- a/cli/js/files_test.ts
+++ b/cli/js/files_test.ts
@@ -21,6 +21,7 @@ testPerm({ read: true }, async function filesCopyToStdout(): Promise<void> {
   const fileSize = Deno.statSync(filename).len;
   assertEquals(bytesWritten, fileSize);
   console.log("bytes written", bytesWritten);
+  file.close();
 });
 
 testPerm({ read: true }, async function filesToAsyncIterator(): Promise<void> {
@@ -33,6 +34,7 @@ testPerm({ read: true }, async function filesToAsyncIterator(): Promise<void> {
   }
 
   assertEquals(totalSize, 12);
+  file.close();
 });
 
 test(async function readerToAsyncIterator(): Promise<void> {
@@ -308,6 +310,7 @@ testPerm({ read: true }, async function seekStart(): Promise<void> {
   await file.read(buf);
   const decoded = new TextDecoder().decode(buf);
   assertEquals(decoded, "world!");
+  file.close();
 });
 
 testPerm({ read: true }, function seekSyncStart(): void {
@@ -321,6 +324,7 @@ testPerm({ read: true }, function seekSyncStart(): void {
   file.readSync(buf);
   const decoded = new TextDecoder().decode(buf);
   assertEquals(decoded, "world!");
+  file.close();
 });
 
 testPerm({ read: true }, async function seekCurrent(): Promise<void> {
@@ -334,6 +338,7 @@ testPerm({ read: true }, async function seekCurrent(): Promise<void> {
   await file.read(buf);
   const decoded = new TextDecoder().decode(buf);
   assertEquals(decoded, "world!");
+  file.close();
 });
 
 testPerm({ read: true }, function seekSyncCurrent(): void {
@@ -347,6 +352,7 @@ testPerm({ read: true }, function seekSyncCurrent(): void {
   file.readSync(buf);
   const decoded = new TextDecoder().decode(buf);
   assertEquals(decoded, "world!");
+  file.close();
 });
 
 testPerm({ read: true }, async function seekEnd(): Promise<void> {
@@ -357,6 +363,7 @@ testPerm({ read: true }, async function seekEnd(): Promise<void> {
   await file.read(buf);
   const decoded = new TextDecoder().decode(buf);
   assertEquals(decoded, "world!");
+  file.close();
 });
 
 testPerm({ read: true }, function seekSyncEnd(): void {
@@ -367,6 +374,7 @@ testPerm({ read: true }, function seekSyncEnd(): void {
   file.readSync(buf);
   const decoded = new TextDecoder().decode(buf);
   assertEquals(decoded, "world!");
+  file.close();
 });
 
 testPerm({ read: true }, async function seekMode(): Promise<void> {
@@ -387,4 +395,5 @@ testPerm({ read: true }, async function seekMode(): Promise<void> {
   const buf = new Uint8Array(1);
   await file.read(buf); // "H"
   assertEquals(new TextDecoder().decode(buf), "H");
+  file.close();
 });
diff --git a/cli/js/net_test.ts b/cli/js/net_test.ts
index 94e7c976e9..8a53a1c742 100644
--- a/cli/js/net_test.ts
+++ b/cli/js/net_test.ts
@@ -112,6 +112,8 @@ testPerm({ net: true }, async function netUdpSendReceive(): Promise<void> {
   assertEquals(1, recvd[0]);
   assertEquals(2, recvd[1]);
   assertEquals(3, recvd[2]);
+  alice.close();
+  bob.close();
 });
 
 testPerm(
diff --git a/cli/js/os_test.ts b/cli/js/os_test.ts
index cdf72fdd7e..6825b7b0df 100644
--- a/cli/js/os_test.ts
+++ b/cli/js/os_test.ts
@@ -76,6 +76,7 @@ if (Deno.build.os === "win") {
         new TextDecoder().decode(await proc.output())
       );
       assertEquals(actualValues, expectedValues);
+      proc.close();
     };
 
     assertEquals(Deno.env("path"), Deno.env("PATH"));
diff --git a/cli/js/process_test.ts b/cli/js/process_test.ts
index fc9d151401..29467cc67c 100644
--- a/cli/js/process_test.ts
+++ b/cli/js/process_test.ts
@@ -299,6 +299,7 @@ testPerm({ run: true }, async function runClose(): Promise<void> {
   const data = new Uint8Array(10);
   const r = await p.stderr!.read(data);
   assertEquals(r, Deno.EOF);
+  p.stderr!.close();
 });
 
 test(function signalNumbers(): void {
@@ -341,6 +342,7 @@ if (Deno.build.os !== "win") {
     // re-enable when it can be made deterministic.
     // assertEquals(status.code, 1);
     // assertEquals(status.signal, Deno.Signal.SIGINT);
+    p.close();
   });
 
   testPerm({ run: true }, async function killFailed(): Promise<void> {
diff --git a/cli/js/resources_test.ts b/cli/js/resources_test.ts
index 5d1e27af71..e3519a2dc5 100644
--- a/cli/js/resources_test.ts
+++ b/cli/js/resources_test.ts
@@ -31,8 +31,9 @@ testPerm({ net: true }, async function resourcesNet(): Promise<void> {
 
 testPerm({ read: true }, async function resourcesFile(): Promise<void> {
   const resourcesBefore = Deno.resources();
-  await Deno.open("cli/tests/hello.txt");
+  const f = await Deno.open("cli/tests/hello.txt");
   const resourcesAfter = Deno.resources();
+  f.close();
 
   // check that exactly one new resource (file) was added
   assertEquals(
diff --git a/cli/js/test_util.ts b/cli/js/test_util.ts
index b8ae3ca93a..6f52c01df2 100644
--- a/cli/js/test_util.ts
+++ b/cli/js/test_util.ts
@@ -106,6 +106,22 @@ function normalizeTestPermissions(perms: TestPermissions): Permissions {
   };
 }
 
+// Wrap `TestFunction` in additional assertion that makes sure
+// the test case does not "leak" resources - ie. resource table after
+// the test has exactly the same contents as before the test.
+function assertResources(fn: Deno.TestFunction): Deno.TestFunction {
+  return async function(): Promise<void> {
+    const preResources = Deno.resources();
+    await fn();
+    const postResources = Deno.resources();
+    const msg = `Test case is leaking resources.
+Before: ${JSON.stringify(preResources, null, 2)}
+After: ${JSON.stringify(postResources, null, 2)}`;
+
+    assertEquals(preResources, postResources, msg);
+  };
+}
+
 export function testPerm(perms: TestPermissions, fn: Deno.TestFunction): void {
   const normalizedPerms = normalizeTestPermissions(perms);
 
@@ -115,7 +131,7 @@ export function testPerm(perms: TestPermissions, fn: Deno.TestFunction): void {
     return;
   }
 
-  Deno.test(fn);
+  Deno.test(fn.name, assertResources(fn));
 }
 
 export function test(fn: Deno.TestFunction): void {
@@ -171,6 +187,24 @@ export async function parseUnitTestOutput(
   return { actual, expected, resultOutput: result };
 }
 
+export interface ResolvableMethods<T> {
+  resolve: (value?: T | PromiseLike<T>) => void;
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  reject: (reason?: any) => void;
+}
+
+export type Resolvable<T> = Promise<T> & ResolvableMethods<T>;
+
+export function createResolvable<T>(): Resolvable<T> {
+  let methods: ResolvableMethods<T>;
+  const promise = new Promise<T>((resolve, reject): void => {
+    methods = { resolve, reject };
+  });
+  // TypeScript doesn't know that the Promise callback occurs synchronously
+  // therefore use of not null assertion (`!`)
+  return Object.assign(promise, methods!) as Resolvable<T>;
+}
+
 test(function permissionsMatches(): void {
   assert(
     permissionsMatch(
@@ -265,28 +299,25 @@ testPerm({ read: true }, async function parsingUnitTestOutput(): Promise<void> {
   let result;
 
   // This is an example of a successful unit test output.
-  result = await parseUnitTestOutput(
-    await Deno.open(`${testDataPath}/unit_test_output1.txt`),
-    false
-  );
+  const f1 = await Deno.open(`${testDataPath}/unit_test_output1.txt`);
+  result = await parseUnitTestOutput(f1, false);
   assertEquals(result.actual, 96);
   assertEquals(result.expected, 96);
+  f1.close();
 
   // This is an example of a silently dying unit test.
-  result = await parseUnitTestOutput(
-    await Deno.open(`${testDataPath}/unit_test_output2.txt`),
-    false
-  );
+  const f2 = await Deno.open(`${testDataPath}/unit_test_output2.txt`);
+  result = await parseUnitTestOutput(f2, false);
   assertEquals(result.actual, undefined);
   assertEquals(result.expected, 96);
+  f2.close();
 
   // This is an example of compiling before successful unit tests.
-  result = await parseUnitTestOutput(
-    await Deno.open(`${testDataPath}/unit_test_output3.txt`),
-    false
-  );
+  const f3 = await Deno.open(`${testDataPath}/unit_test_output3.txt`);
+  result = await parseUnitTestOutput(f3, false);
   assertEquals(result.actual, 96);
   assertEquals(result.expected, 96);
+  f3.close();
 
   // Check what happens on empty output.
   const f = new Deno.Buffer(new TextEncoder().encode("\n\n\n"));
diff --git a/cli/js/tls_test.ts b/cli/js/tls_test.ts
index 6983212749..0fb4cbb7b5 100644
--- a/cli/js/tls_test.ts
+++ b/cli/js/tls_test.ts
@@ -1,5 +1,11 @@
 // Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
-import { test, testPerm, assert, assertEquals } from "./test_util.ts";
+import {
+  test,
+  testPerm,
+  assert,
+  assertEquals,
+  createResolvable
+} from "./test_util.ts";
 import { BufWriter, BufReader } from "../../std/io/bufio.ts";
 import { TextProtoReader } from "../../std/textproto/mod.ts";
 
@@ -142,6 +148,7 @@ testPerm(
 testPerm({ read: true, net: true }, async function dialAndListenTLS(): Promise<
   void
 > {
+  const resolvable = createResolvable();
   const hostname = "localhost";
   const port = 4500;
 
@@ -164,6 +171,7 @@ testPerm({ read: true, net: true }, async function dialAndListenTLS(): Promise<
       // TODO(bartlomieju): this might be a bug
       setTimeout(() => {
         conn.close();
+        resolvable.resolve();
       }, 0);
     }
   );
@@ -196,4 +204,6 @@ testPerm({ read: true, net: true }, async function dialAndListenTLS(): Promise<
   await r.readFull(bodyBuf);
   assertEquals(decoder.decode(bodyBuf), "Hello World\n");
   conn.close();
+  listener.close();
+  await resolvable;
 });
diff --git a/cli/js/tty_test.ts b/cli/js/tty_test.ts
index f58784a7cd..0346178845 100644
--- a/cli/js/tty_test.ts
+++ b/cli/js/tty_test.ts
@@ -7,6 +7,7 @@ testPerm({ read: true }, function isatty(): void {
   // CI not under TTY, so cannot test stdin/stdout/stderr.
   const f = Deno.openSync("cli/tests/hello.txt");
   assert(!Deno.isatty(f.rid));
+  f.close();
 });
 
 test(function isattyError(): void {
diff --git a/cli/js/workers_test.ts b/cli/js/workers_test.ts
index 7dbd316ec4..5b8b1ef974 100644
--- a/cli/js/workers_test.ts
+++ b/cli/js/workers_test.ts
@@ -1,23 +1,11 @@
 // Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
-import { test, testPerm, assert, assertEquals } from "./test_util.ts";
-
-export interface ResolvableMethods<T> {
-  resolve: (value?: T | PromiseLike<T>) => void;
-  // eslint-disable-next-line @typescript-eslint/no-explicit-any
-  reject: (reason?: any) => void;
-}
-
-export type Resolvable<T> = Promise<T> & ResolvableMethods<T>;
-
-export function createResolvable<T>(): Resolvable<T> {
-  let methods: ResolvableMethods<T>;
-  const promise = new Promise<T>((resolve, reject): void => {
-    methods = { resolve, reject };
-  });
-  // TypeScript doesn't know that the Promise callback occurs synchronously
-  // therefore use of not null assertion (`!`)
-  return Object.assign(promise, methods!) as Resolvable<T>;
-}
+import {
+  test,
+  testPerm,
+  assert,
+  assertEquals,
+  createResolvable
+} from "./test_util.ts";
 
 test(async function workersBasic(): Promise<void> {
   const promise = createResolvable();