diff --git a/package.json b/package.json
index 07c258d..6e4b90e 100644
--- a/package.json
+++ b/package.json
@@ -29,7 +29,7 @@
   "scripts": {
     "start": "webpack serve --open --env mode=development",
     "build": "rm -rf dist && webpack --env mode=production",
-    "format": "prettier --write src/*.ts src/*.tsx src/*.css",
+    "format": "prettier --write src/*.ts src/*.tsx src/*.css src/browser-unit.html",
     "typecheck": "tsc --noEmit"
   },
   "dependencies": {
diff --git a/src/blog-cells.tsx b/src/blog-cells.tsx
index 03f7309..977a6e4 100644
--- a/src/blog-cells.tsx
+++ b/src/blog-cells.tsx
@@ -192,27 +192,27 @@ class Cell extends React.Component<
       setTimeout(() => resolve(), 500);
     });
 
-    this.props.kernel.run(
-      code,
-      (line) => {
-        this.setState((state) => {
-          state.output.push(line);
-          return state;
-        });
-      },
-      async () => {
-        // Wait the minimum amount of run-time.
-        await minimumWait;
-
-        this.running = false;
-        this.setState((state) => {
-          state.kind = "re-runnable";
-          if (state.output.length === 0)
-            state.output.push({ type: "log", line: "Done." });
-          return state;
-        });
-      }
-    );
+    // Run the code.
+    await this.props.kernel.run(code, (line) => {
+      this.setState((state) => {
+        state.output.push(line);
+        return state;
+      });
+    });
+
+    // Wait the minimum amount of run-time.
+    await minimumWait;
+
+    // Mark as not running.
+    this.running = false;
+
+    // Update the state.
+    this.setState((state) => {
+      state.kind = "re-runnable";
+      if (state.output.length === 0)
+        state.output.push({ type: "log", line: "Done." });
+      return state;
+    });
   }
 }
 
diff --git a/src/browser-unit.html b/src/browser-unit.html
index 0e26163..345fd4f 100644
--- a/src/browser-unit.html
+++ b/src/browser-unit.html
@@ -16,36 +16,88 @@
     <script type="module" src="./blog-cells.js"></script>
 
     <script class="mocha-init">
-      mocha.setup('bdd');
+      mocha.setup("bdd");
+      chai.config.truncateThreshold = 0;
     </script>
     <script class="mocha-exec" type="module">
       describe("JavaScriptKernel", () => {
-        it("Runs basic code.", (done) => {
-            const kernel = new BlogCells.JavaScriptKernel();
-            const onOutput = chai.spy();
-            kernel.run("console.log('Hello World!');", onOutput, () => {
-                chai.expect(onOutput).to.have.been.called.with({
-                  type: "log",
-                  line: "Hello World!"
-                });
-
-                done();
-            });
+        it("Runs basic code.", async () => {
+          const kernel = new BlogCells.JavaScriptKernel();
+          const onOutput = chai.spy();
+          await kernel.run("console.log('Hello World!');", onOutput);
+
+          chai.expect(onOutput).to.have.been.called.with({
+            type: "log",
+            line: "Hello World!",
+          });
+        });
+
+        it("Allows defining code across cells.", async () => {
+          const kernel = new BlogCells.JavaScriptKernel();
+          const onOutput = chai.spy();
+          await kernel.run(
+            `export function hello() { return "Hello World!"; }`,
+            onOutput
+          );
+          await kernel.run(`console.log(hello());`, onOutput);
+
+          chai.expect(onOutput).to.have.been.called.with({
+            type: "log",
+            line: "Hello World!",
+          });
         });
       });
 
       describe("PythonKernel", () => {
-        it("Runs basic code.", (done) => {
-            const kernel = new BlogCells.PythonKernel();
-            const onOutput = chai.spy();
-            kernel.run("print('Hello World!');", onOutput, () => {
-                chai.expect(onOutput).to.have.been.called.with({
-                  type: "log",
-                  line: "Hello World!"
-                });
-
-                done();
-            });
+        it("Runs basic code.", async () => {
+          const kernel = new BlogCells.PythonKernel();
+          const onOutput = chai.spy();
+          await kernel.run("print('Hello World!');", onOutput);
+
+          chai.expect(onOutput).to.have.been.called.with({
+            type: "log",
+            line: "Hello World!",
+          });
+        }).timeout(10 * 1000);
+
+        it("Allows defining code across cells.", async () => {
+          const kernel = new BlogCells.PythonKernel();
+          const onOutput = chai.spy();
+          await kernel.run(`def hello(): return "Hello World!"`, onOutput);
+          await kernel.run(`print(hello())`, onOutput);
+
+          chai.expect(onOutput).to.have.been.called.with({
+            type: "log",
+            line: "Hello World!",
+          });
+        }).timeout(10 * 1000);
+
+        it("Allows importing packages with micropip.", async () => {
+          const kernel = new BlogCells.PythonKernel();
+          const onOutput = chai.spy();
+          await kernel.run(
+            `import micropip; await micropip.install("numpy")`,
+            onOutput
+          );
+          await kernel.run(
+            `import numpy as np; print(np.zeros(shape=(3, 3)))`,
+            onOutput
+          );
+
+          console.log(onOutput);
+
+          chai.expect(onOutput).on.nth(1).been.called.with({
+            type: "log",
+            line: "[[0. 0. 0.]",
+          });
+          chai.expect(onOutput).on.nth(2).been.called.with({
+            type: "log",
+            line: " [0. 0. 0.]",
+          });
+          chai.expect(onOutput).on.nth(3).been.called.with({
+            type: "log",
+            line: " [0. 0. 0.]]",
+          });
         }).timeout(10 * 1000);
       });
 
diff --git a/src/javascript-kernel/index.ts b/src/javascript-kernel/index.ts
index acff154..3d7e1d0 100644
--- a/src/javascript-kernel/index.ts
+++ b/src/javascript-kernel/index.ts
@@ -23,29 +23,31 @@ export type ExecutionResponse = {
 export class JavaScriptKernel extends Kernel {
     worker: Worker = new Worker(URL.createObjectURL(blob));
 
-    run(code: string, onOutput: (line: OutputLine) => void, onDone: () => void) {
+    run(code: string, onOutput: (line: OutputLine) => void): Promise<void> {
         // Generate a unique ID to track this execution request.
         const requestID = this.getRequestID();
 
-        const messageHandler = (e: MessageEvent<ExecutionResponse>) => {
-            if (e.data.requestID != requestID) return;
-
-            if (e.data.kind === "run-code-output") {
-                onOutput(e.data.output);
-            } else if (e.data.kind === "run-code-done") {
-                this.worker.removeEventListener("message", messageHandler);
-                onDone();
-            }
-        };
-
-        this.worker.addEventListener("message", messageHandler);
-
-        // Post the code to the worker.
-        this.worker.postMessage({
-            kind: "run-code",
-            code: code,
-            requestID: requestID,
-        } as ExecutionRequest);
+        return new Promise<void>((resolve) => {
+            const messageHandler = (e: MessageEvent<ExecutionResponse>) => {
+                if (e.data.requestID != requestID) return;
+    
+                if (e.data.kind === "run-code-output") {
+                    onOutput(e.data.output);
+                } else if (e.data.kind === "run-code-done") {
+                    this.worker.removeEventListener("message", messageHandler);
+                    resolve();
+                }
+            };
+
+            this.worker.addEventListener("message", messageHandler);
+
+            // Post the code to the worker.
+            this.worker.postMessage({
+                kind: "run-code",
+                code: code,
+                requestID: requestID,
+            } as ExecutionRequest);
+        });
     }
 
     getSyntaxHighlighter() {
diff --git a/src/kernel.ts b/src/kernel.ts
index eefb83e..27c69cd 100644
--- a/src/kernel.ts
+++ b/src/kernel.ts
@@ -13,8 +13,8 @@ export abstract class Kernel {
 
   abstract run(
     code: string,
-    onOutput: (line: OutputLine) => void,
-    onDone: () => void
-  );
+    onOutput: (line: OutputLine) => void
+  ): Promise<void>;
+
   abstract getSyntaxHighlighter(): LanguageSupport;
 }
diff --git a/src/python-kernel/index.ts b/src/python-kernel/index.ts
index 6311257..5a00923 100644
--- a/src/python-kernel/index.ts
+++ b/src/python-kernel/index.ts
@@ -8,28 +8,30 @@ import { Kernel, OutputLine } from "../kernel";
 export class PythonKernel extends Kernel {
     worker: Worker = new Worker(URL.createObjectURL(blob));
 
-    run(code: string, onOutput: (line: OutputLine) => void, onDone: () => void) {
+    run(code: string, onOutput: (line: OutputLine) => void): Promise<void> {
         // Generate a unique ID to track this execution request.
         const requestID = this.getRequestID();
 
-        const messageHandler = (e: MessageEvent) => {
-            if (e.data.requestID != requestID) return;
-
-            if (e.data.kind === "run-code-output") {
-                onOutput(e.data.output);
-            } else if (e.data.kind === "run-code-done") {
-                this.worker.removeEventListener("message", messageHandler);
-                onDone();
-            }
-        };
-
-        this.worker.addEventListener("message", messageHandler);
-
-        // Post the code to the worker.
-        this.worker.postMessage({
-            kind: "run-code",
-            code: code,
-            requestID: requestID,
+        return new Promise<void>((resolve) => {
+            const messageHandler = (e: MessageEvent) => {
+                if (e.data.requestID != requestID) return;
+    
+                if (e.data.kind === "run-code-output") {
+                    onOutput(e.data.output);
+                } else if (e.data.kind === "run-code-done") {
+                    this.worker.removeEventListener("message", messageHandler);
+                    resolve();
+                }
+            };
+    
+            this.worker.addEventListener("message", messageHandler);
+    
+            // Post the code to the worker.
+            this.worker.postMessage({
+                kind: "run-code",
+                code: code,
+                requestID: requestID,
+            });
         });
     }