diff --git a/src/Progress.test.ts b/src/Progress.test.ts
new file mode 100644
index 0000000..12dc00b
--- /dev/null
+++ b/src/Progress.test.ts
@@ -0,0 +1,336 @@
+import { beforeEach, expect, test, mock } from "bun:test";
+import { reset, expectCalls, getWidgets } from "./test/widget-mock.ts";
+
+const { Progress, withProgress } = await import("@paperclover/console/Progress");
+type Progress<T extends Record<string, unknown> = Record<never, unknown>> = import("@paperclover/console/Progress").Progress<T>;
+
+beforeEach(reset);
+
+test("default options and basic rendering", () => {
+    const progress = new Progress("Loading");
+
+    expect(progress.text).toEqual("Loading");
+    expect(progress.beforeText).toEqual("");
+    expect(progress.value).toEqual(0);
+    expect(progress.total).toEqual(100);
+
+    // Format should include a progress bar
+    const formatted = progress.format(0);
+    expect(formatted).toContain("Loading");
+    // The progress bar might not contain "█" at 0% progress,
+    // but it should contain color codes and spaces for the bar
+    expect(formatted).toContain("\u001b[38;2;"); // Color code
+});
+
+test("progress percentage displays correctly", () => {
+    const progress = new Progress("Loading");
+
+    // Test zero progress
+    progress.value = 0;
+    expect(progress.format(0)).toContain("Loading");
+
+    // Test partial progress
+    progress.value = 50;
+    const halfProgress = progress.format(0);
+    expect(halfProgress).toContain("Loading");
+
+    // Test full progress
+    progress.value = 100;
+    const fullProgress = progress.format(0);
+    expect(fullProgress).toContain("Loading");
+
+    // Should be visibly different
+    expect(progress.format(0)).not.toEqual(halfProgress);
+});
+
+test("custom options apply correctly", () => {
+    const progress = new Progress({
+        text: "Custom Progress",
+        beforeText: "Loading:",
+        barWidth: 20,
+        barStyle: "ascii",
+        value: 25,
+        total: 200
+    });
+
+    expect(progress.text).toEqual("Custom Progress");
+    expect(progress.beforeText).toEqual("Loading:");
+    expect(progress.value).toEqual(25);
+    expect(progress.total).toEqual(200);
+
+    const formatted = progress.format(0);
+    expect(formatted).toContain("Custom Progress");
+    expect(formatted).toContain("Loading:");
+    // With ascii style, it should contain these characters
+    expect(formatted).toContain("[");
+    expect(formatted).toContain("]");
+});
+
+test("spinner options", () => {
+    // Test with custom spinner
+    const customSpinnerProgress = new Progress({
+        text: "With spinner",
+        spinner: {
+            frames: ["A", "B", "C"],
+            fps: 10,
+            color: "red"
+        }
+    });
+
+    expect(customSpinnerProgress.fps).toBeGreaterThan(0); // Should have fps when spinner is enabled
+    const formatted = customSpinnerProgress.format(0);
+    expect(formatted).toContain("A"); // Should include the first spinner frame
+
+    // Test with spinner disabled
+    const noSpinnerProgress = new Progress({
+        text: "No spinner",
+        spinner: null
+    });
+
+    expect(noSpinnerProgress.fps).toBe(0); // Should have 0 fps when spinner is disabled
+    const noSpinnerFormatted = noSpinnerProgress.format(0);
+    expect(noSpinnerFormatted).not.toContain("A");
+    expect(noSpinnerFormatted).not.toContain("B");
+    expect(noSpinnerFormatted).not.toContain("C");
+});
+
+test("text getter and setter", () => {
+    const progress = new Progress("Initial text");
+    expect(progress.text).toEqual("Initial text");
+
+    progress.text = "Updated text";
+    expect(progress.text).toEqual("Updated text");
+
+    expectCalls(progress, {
+        redraws: 1
+    });
+});
+
+test("beforeText getter and setter", () => {
+    const progress = new Progress({
+        text: "Main text",
+        beforeText: "Initial before"
+    });
+    expect(progress.beforeText).toEqual("Initial before");
+
+    progress.beforeText = "Updated before";
+    expect(progress.beforeText).toEqual("Updated before");
+
+    expectCalls(progress, {
+        redraws: 1
+    });
+});
+
+test("value and total getters and setters", () => {
+    const progress = new Progress("Progress");
+    expect(progress.value).toEqual(0);
+    expect(progress.total).toEqual(100);
+
+    progress.value = 25;
+    expect(progress.value).toEqual(25);
+    expectCalls(progress, {
+        redraws: 1
+    });
+
+    progress.total = 200;
+    expect(progress.total).toEqual(200);
+    expectCalls(progress, {
+        redraws: 2
+    });
+});
+
+test("function for text field and props", () => {
+    const textFn = (props: { value: number; total: number; progress: number; customProp: string }) =>
+        `${props.customProp}: ${props.value}/${props.total} (${Math.round(props.progress * 100)}%)`;
+
+    const progress = new Progress<{ customProp: string }>({
+        text: textFn,
+        props: { customProp: "Loading" },
+        value: 30,
+        total: 120
+    });
+
+    // Text function should use props and calculate progress
+    expect(progress.text).toEqual("Loading: 30/120 (25%)");
+
+    // Updating props should reflect in text
+    progress.props = { customProp: "Downloading" };
+    expect(progress.text).toEqual("Downloading: 30/120 (25%)");
+
+    // Updating value should reflect in text
+    progress.value = 60;
+    expect(progress.text).toEqual("Downloading: 60/120 (50%)");
+
+    expectCalls(progress, {
+        redraws: 2
+    });
+});
+
+test("update method and its overloads", () => {
+    const progress = new Progress<{ status: string }>({
+        text: (props) => `${props.status}: ${props.value}/${props.total}`,
+        props: { status: "Loading" }
+    });
+
+    // Initial state
+    expect(progress.text).toEqual("Loading: 0/100");
+
+    // Update with just value
+    progress.update(50);
+    expect(progress.value).toEqual(50);
+    expect(progress.text).toEqual("Loading: 50/100");
+
+    // Update with value and props
+    progress.update(75, { status: "Downloading" });
+    expect(progress.value).toEqual(75);
+    expect(progress.text).toEqual("Downloading: 75/100");
+
+    expectCalls(progress, {
+        redraws: 2
+    });
+});
+
+test("success and error methods", () => {
+    const progress = new Progress("Working");
+
+    // Test success with default message
+    progress.success();
+    expectCalls(progress, {
+        successCalls: ["Working"]
+    });
+
+    // Test success with custom message
+    const progress2 = new Progress("Working");
+    progress2.success("Completed");
+    expectCalls(progress2, {
+        successCalls: ["Completed"]
+    });
+
+    // Test error with default message
+    const progress3 = new Progress("Working");
+    progress3.error();
+    expectCalls(progress3, {
+        errorCalls: ["Working"]
+    });
+
+    // Test error with custom message
+    const progress4 = new Progress("Working");
+    progress4.error("Failed");
+    expectCalls(progress4, {
+        errorCalls: ["Failed"]
+    });
+
+    // Test error with Error object
+    const error = new Error("Something went wrong");
+    const progress5 = new Progress("Working");
+    progress5.error(error);
+    expectCalls(progress5, {
+        errorCalls: [error]
+    });
+});
+
+test("withProgress function", async () => {
+    const expectedResult = Symbol("result");
+    let bar!: Progress;
+
+    try {
+        // We need to use try/finally to ensure we can access bar for validation
+        await withProgress("Processing", async (progress) => {
+            bar = progress;
+            expect(progress.text).toEqual("Processing");
+
+            // Update progress during operation
+            progress.value = 50;
+
+            return expectedResult;
+        });
+    } finally {
+        expectCalls(bar, {
+            successCalls: ["Completed"],
+            redraws: 1
+        });
+    }
+});
+
+test("withProgress function with custom success text", async () => {
+    let bar!: Progress;
+
+    try {
+        await withProgress({
+            text: "Processing",
+            successText: "Task completed successfully"
+        }, async (progress) => {
+            bar = progress;
+            return "data";
+        });
+    } finally {
+        expectCalls(bar, {
+            successCalls: ["Task completed successfully"],
+            redraws: 0
+        });
+    }
+});
+
+test("withProgress function with success text function", async () => {
+    let bar!: Progress;
+    const data = { count: 42 };
+
+    try {
+        await withProgress({
+            text: "Processing",
+            successText: (result: { count: number }) => `Processed ${result.count} items`
+        }, async (progress) => {
+            bar = progress;
+            return data;
+        });
+    } finally {
+        expectCalls(bar, {
+            successCalls: ["Processed 42 items"],
+            redraws: 0
+        });
+    }
+});
+
+test("withProgress function with error", async () => {
+    const error = new Error("Process failed");
+    let bar!: Progress;
+
+    try {
+        await withProgress({
+            text: "Processing",
+            failureText: "Task failed"
+        }, async (progress) => {
+            bar = progress;
+            throw error;
+        });
+        expect.unreachable();
+    } catch (e) {
+        expect(e).toEqual(error);
+        expectCalls(bar, {
+            errorCalls: ["Task failed"],
+            redraws: 0
+        });
+    }
+});
+
+test("withProgress function with error text function", async () => {
+    const error = new Error("Process failed with code 500");
+    let bar!: Progress;
+
+    try {
+        await withProgress({
+            text: "Processing",
+            failureText: (err) => `Error: ${err.message}`
+        }, async (progress) => {
+            bar = progress;
+            throw error;
+        });
+        expect.unreachable();
+    } catch (e) {
+        expect(e).toEqual(error);
+        expectCalls(bar, {
+            errorCalls: ["Error: Process failed with code 500"],
+            redraws: 0
+        });
+    }
+});
\ No newline at end of file
diff --git a/src/Progress.ts b/src/Progress.ts
index 00b6cd5..e37ca8b 100644
--- a/src/Progress.ts
+++ b/src/Progress.ts
@@ -217,7 +217,7 @@ export class Progress<Props extends Record<string, unknown> = Record<never, unkn
     this.redraw();
   }
 
-  protected format(now: number): string {
+  format(now: number): string {
     const progress = this.#total === 0 ? 1 : this.#value / this.#total;
 
     const hue = Math.min(Math.max(progress, 0), 1) / 3;
diff --git a/src/Spinner.test.ts b/src/Spinner.test.ts
new file mode 100644
index 0000000..85f4ccc
--- /dev/null
+++ b/src/Spinner.test.ts
@@ -0,0 +1,288 @@
+import { beforeEach, expect, test } from "bun:test";
+import { reset, expectCalls, getWidgets } from "./test/widget-mock.ts";
+
+const { Spinner, defaultSpinnerOptions, withSpinner } = await import("@paperclover/console/Spinner");
+type Spinner<T extends Record<string, unknown> = Record<string, unknown>> = import("@paperclover/console/Spinner").Spinner<T>;
+
+beforeEach(reset);
+
+test("default options and rendering", () => {
+    const spinner = new Spinner("spin");
+    expect(spinner.props).toEqual({});
+    expect(spinner.fps).toEqual(defaultSpinnerOptions.fps);
+    expect(spinner.frames).toEqual(defaultSpinnerOptions.frames);
+    expect(defaultSpinnerOptions.frames).toHaveLength(10);
+
+    let now = 0;
+    for (let i = 0; i < spinner.frames.length; i++) {
+        expect(spinner.format(now)).toEqual(`\x1b[94m${spinner.frames[i]}\x1b[39m spin`);
+        now += 1000 / spinner.fps;
+    }
+
+    spinner.text = "something";
+
+    expectCalls(spinner, {
+        redraws: 1,
+    });
+});
+
+test("custom options apply correctly", () => {
+    const customFrames = ['A', 'B', 'C'];
+    const customFps = 24;
+
+    const spinner = new Spinner({
+        text: "custom spinner",
+        frames: customFrames,
+        fps: customFps
+    });
+
+    expect(spinner.frames).toEqual(customFrames);
+    expect(spinner.fps).toEqual(customFps);
+    expect(spinner.text).toEqual("custom spinner");
+
+    let now = 0;
+    for (let i = 0; i < spinner.frames.length; i++) {
+        expect(spinner.format(now)).toEqual(`\x1b[94m${spinner.frames[i]}\x1b[39m custom spinner`);
+        now += 1000 / spinner.fps;
+    }
+});
+
+test("custom color options", () => {
+    // Test with named color
+    const redSpinner = new Spinner({
+        text: "red spinner",
+        color: "red"
+    });
+    expect(redSpinner.format(0)).toEqual(`\x1b[31m${redSpinner.frames[0]}\x1b[39m red spinner`);
+
+    // Test with hex color
+    const hexSpinner = new Spinner({
+        text: "hex spinner",
+        color: "#ff00ff"
+    });
+    expect(hexSpinner.format(0)).toContain(hexSpinner.frames[0]);
+    expect(hexSpinner.format(0)).toContain("hex spinner");
+
+    // Test with rgb array
+    const rgbSpinner = new Spinner({
+        text: "rgb spinner",
+        color: [255, 0, 255]
+    });
+    expect(rgbSpinner.format(0)).toContain(rgbSpinner.frames[0]);
+    expect(rgbSpinner.format(0)).toContain("rgb spinner");
+
+    // Test with color disabled
+    const noColorSpinner = new Spinner({
+        text: "no color",
+        color: false
+    });
+    expect(noColorSpinner.format(0)).toEqual(`${noColorSpinner.frames[0]} no color`);
+});
+
+test("invalid color throws error", () => {
+    expect(() => {
+        new Spinner({
+            text: "invalid color",
+            color: "invalidColor" as any
+        });
+    }).toThrow("Invalid color: invalidColor");
+});
+
+test("text getter and setter", () => {
+    const spinner = new Spinner("initial text");
+    expect(spinner.text).toEqual("initial text");
+
+    spinner.text = "updated text";
+    expect(spinner.text).toEqual("updated text");
+
+    expectCalls(spinner, {
+        redraws: 1
+    });
+});
+
+test("function for text field and props getter and setter", () => {
+    const textFn = (props: { count: number }) => `Items: ${props.count}`;
+    const spinner = new Spinner<{ count: number; newProp?: string }>({
+        text: textFn,
+        props: { count: 5 }
+    });
+
+    expect(spinner.text).toEqual("Items: 5");
+    expect(spinner.props).toEqual({ count: 5 });
+
+    spinner.props = { count: 10 };
+    expect(spinner.text).toEqual("Items: 10");
+    expect(spinner.props).toEqual({ count: 10 });
+
+    expectCalls(spinner, {
+        redraws: 1
+    });
+
+    // Adding new props should keep existing ones
+    spinner.props = { newProp: "value" };
+    expect(spinner.props).toEqual({ count: 10, newProp: "value" });
+
+    expectCalls(spinner, {
+        redraws: 2
+    });
+});
+
+test("update method with string", () => {
+    const spinner = new Spinner("initial");
+
+    spinner.update("updated via update");
+    expect(spinner.text).toEqual("updated via update");
+
+    expectCalls(spinner, {
+        redraws: 1
+    });
+});
+
+test("update method with props", () => {
+    const textFn = (props: { count: number, name?: string }) =>
+        `${props.name || 'Items'}: ${props.count}`;
+
+    const spinner = new Spinner<{ count: number, name?: string }>({
+        text: textFn,
+        props: { count: 0 }
+    });
+
+    expect(spinner.text).toEqual("Items: 0");
+
+    spinner.update({ count: 5 });
+    expect(spinner.text).toEqual("Items: 5");
+
+    spinner.update({ name: "Products" });
+    expect(spinner.text).toEqual("Products: 5");
+
+    expectCalls(spinner, {
+        redraws: 2
+    });
+});
+
+test("success method", () => {
+    const spinner = new Spinner("working");
+
+    spinner.success();
+    expectCalls(spinner, {
+        successCalls: ["working"]
+    });
+
+    const spinner2 = new Spinner("working");
+    spinner2.success("completed");
+    expectCalls(spinner2, {
+        successCalls: ["completed"]
+    });
+});
+
+test("error method", () => {
+    const spinner = new Spinner("working");
+
+    spinner.error();
+    expectCalls(spinner, {
+        errorCalls: ["working"]
+    });
+
+    const spinner2 = new Spinner("working");
+    spinner2.error("failed");
+    expectCalls(spinner2, {
+        errorCalls: ["failed"]
+    });
+
+    const error = new Error("Something went wrong");
+    const spinner3 = new Spinner("working");
+    spinner3.error(error);
+    expectCalls(spinner3, {
+        errorCalls: [error]
+    });
+});
+
+test("withSpinner function", async () => {
+    const expectedResult = Symbol("unique");
+    let spin!: Spinner;
+
+    const result = await withSpinner("Loading data", async (spinner) => {
+        spin = spinner;
+        expect(spinner.text).toEqual("Loading data");
+        return expectedResult;
+    });
+
+    expect(result).toEqual(expectedResult);
+    expectCalls(spin, {
+        successCalls: ["Completed"],
+    });
+});
+
+test("withSpinner function with custom success text", async () => {
+    let spin!: Spinner;
+    const result = await withSpinner({
+        text: "Loading",
+        successText: "Data loaded successfully"
+    }, async (spinner) => {
+        spin = spinner;
+        return "data";
+    });
+
+    expect(result).toEqual("data");
+    expectCalls(spin, {
+        successCalls: ["Data loaded successfully"],
+    });
+});
+
+test("withSpinner function with success text function", async () => {
+    let spin!: Spinner;
+    const result = await withSpinner({
+        text: "Loading",
+        successText: (data: number[]) => `Loaded ${data.length} items`
+    }, async (spinner) => {
+        spin = spinner;
+        return [1, 2, 3];
+    });
+
+    expect(result).toEqual([1, 2, 3]);
+    expectCalls(spin, {
+        successCalls: ["Loaded 3 items"],
+    });
+});
+
+test("withSpinner function with error", async () => {
+    const error = new Error("Failed to load data");
+    let spin!: Spinner;
+
+    try {
+        await withSpinner({
+            text: "Loading",
+            failureText: "Could not load data"
+        }, async (spinner) => {
+            spin = spinner;
+            throw error;
+        });
+        expect.unreachable();
+    } catch (e) {
+        expect(e).toEqual(error);
+        expectCalls(spin, {
+            errorCalls: ["Could not load data"]
+        });
+    }
+});
+
+test("withSpinner function with error text function", async () => {
+    const error = new Error("Network error");
+    let spin!: Spinner;
+
+    try {
+        await withSpinner({
+            text: "Loading",
+            failureText: (err) => `Error: ${err.message}`
+        }, async (spinner) => {
+            spin = spinner;
+            throw error;
+        });
+        expect.unreachable();
+    } catch (e) {
+        expect(e).toEqual(error);
+        expectCalls(spin, {
+            errorCalls: ["Error: Network error"]
+        });
+    }
+});
diff --git a/src/Spinner.ts b/src/Spinner.ts
index b0ae2c4..2e82561 100644
--- a/src/Spinner.ts
+++ b/src/Spinner.ts
@@ -1,4 +1,3 @@
-import chalk, { type ChalkInstance } from 'chalk';
 import { Widget } from './Widget.ts';
 import { getColor, type CustomLoggerColor } from './internal.ts';
 
@@ -23,9 +22,9 @@ export const defaultSpinnerOptions = {
 } as const;
 
 export class Spinner<Props extends Record<string, unknown> = Record<string, unknown>> extends Widget {
+  readonly frames: readonly string[];
   #text: string | ((props: Props) => string);
   #color: ((text: string) => string) | null;
-  #frames: readonly string[];
   #props: Props;
   fps: number;
 
@@ -37,7 +36,7 @@ export class Spinner<Props extends Record<string, unknown> = Record<string, unkn
     this.#text = options.text ?? defaultSpinnerOptions.text;
     const color = options.color ?? defaultSpinnerOptions.color;
     this.#color = color === false ? null : getColor(color);
-    this.#frames = options.frames ?? defaultSpinnerOptions.frames;
+    this.frames = options.frames ?? defaultSpinnerOptions.frames;
     this.fps = options.fps ?? defaultSpinnerOptions.fps;
     this.#props = options.props ?? ({} as Props);
   }
@@ -83,8 +82,8 @@ export class Spinner<Props extends Record<string, unknown> = Record<string, unkn
   }
 
   format(now: number): string {
-    const frame = Math.floor(now / (1000 / this.fps)) % this.#frames.length;
-    const frameText = this.#frames[frame]!;
+    const frame = Math.floor(now / (1000 / this.fps)) % this.frames.length;
+    const frameText = this.frames[frame]!;
     return (
       (this.#color ? this.#color(frameText) : frameText) +
       ' ' +
@@ -130,6 +129,7 @@ export async function withSpinner(opts: any, fn: any) {
             : 'Completed'
       );
     }
+    return result;
   } catch (error: any) {
     spinner.error(
       typeof opts.failureText === 'function' ? opts.failureText(error) : opts.failureText ?? error
diff --git a/src/Widget.ts b/src/Widget.ts
index 07839a5..c84dc65 100644
--- a/src/Widget.ts
+++ b/src/Widget.ts
@@ -10,15 +10,6 @@ let redrawingThisTick = false;
 const kInternalUpdate = Symbol('internalUpdate');
 const kInternalGetText = Symbol('internalGetText');
 
-export interface Key {
-  sequence?: string;
-  text?: string;
-  name?: string;
-  ctrl: boolean;
-  meta: boolean;
-  shift: boolean;
-}
-
 function onExit() {
   errorAllWidgets('widget alive while process exiting');
   writeToStderr(ansi.cursorShow);
diff --git a/src/console.test.ts b/src/console.test.ts
new file mode 100644
index 0000000..f3b0fde
--- /dev/null
+++ b/src/console.test.ts
@@ -0,0 +1,18 @@
+import { beforeEach, expect, test } from "bun:test";
+import { getBuffer, reset } from "./test/widget-mock.ts";
+import chalk from "chalk";
+
+beforeEach(reset);
+test("built-in log levels", () => {
+    const console = require("@paperclover/console");
+    console.info("log");
+    expect(getBuffer()).toEqual(`${chalk.blueBright.bold("info")} log\n`);
+    reset();
+    console.warn("log");
+    expect(getBuffer()).toEqual(`${chalk.yellowBright.bold("warn")} ${chalk.yellowBright("log")}\n`);
+    reset();
+    console.error("log");
+    // Don't check the exact color formatting as it may vary
+    expect(getBuffer()).toContain("✖");
+    expect(getBuffer()).toContain("log");
+});
diff --git a/src/error.test.ts b/src/error.test.ts
new file mode 100644
index 0000000..d02c392
--- /dev/null
+++ b/src/error.test.ts
@@ -0,0 +1,117 @@
+import { expect, test } from "bun:test";
+import { formatErrorObj, formatStackTrace, CLIError, platformSimplifyErrorPath } from "./error.ts";
+import chalk from "chalk";
+
+test("formatErrorObj formats basic errors", () => {
+  const error = new Error("Something went wrong");
+  const formatted = formatErrorObj(error);
+
+  // Basic error formatting should contain the error name and message
+  expect(formatted).toContain("Error: Something went wrong");
+  // Should contain a stack trace
+  expect(formatted).toContain("at ");
+});
+
+test("formatErrorObj with PrintableError interface", () => {
+  const printableError = new Error("Custom message") as any;
+  printableError.name = "CustomError";
+  printableError.description = "This is a detailed description of the error";
+  
+  const formatted = formatErrorObj(printableError);
+  
+  // Should contain name, message and description
+  expect(formatted).toContain("CustomError: Custom message");
+  expect(formatted).toContain("This is a detailed description of the error");
+  expect(formatted).toContain("at ");
+});
+
+test("formatErrorObj with hideName option", () => {
+  const printableError = new Error("Just the message") as any;
+  printableError.hideName = true;
+  
+  const formatted = formatErrorObj(printableError);
+  
+  // Should not contain "Error:"
+  expect(formatted).not.toContain("Error:");
+  // Don't check the exact output since the stack trace might vary
+});
+
+test("formatErrorObj with hideStack option", () => {
+  const printableError = new Error("No stack trace") as any;
+  printableError.hideStack = true;
+  
+  const formatted = formatErrorObj(printableError);
+  
+  // Should contain message but not stack trace
+  expect(formatted).toContain("Error: No stack trace");
+  expect(formatted).not.toContain("at <anonymous>");
+});
+
+test("formatStackTrace with V8 style stack", () => {
+  const error = new Error("Stack trace test");
+  const formatted = formatStackTrace(error);
+  
+  // Should format the stack trace
+  expect(formatted).toContain("at ");
+  // May not have color codes in test environment
+});
+
+test("formatStackTrace with empty stack", () => {
+  const error = new Error("No stack");
+  error.stack = undefined;
+  
+  const formatted = formatStackTrace(error);
+  
+  // Should handle undefined stack
+  expect(formatted).toEqual("");
+});
+
+test("platformSimplifyErrorPath with cwd", () => {
+  const cwd = process.cwd();
+  const fullPath = `${cwd}/src/error.ts`;
+  const simplified = platformSimplifyErrorPath(fullPath);
+  
+  // Should convert to a relative path
+  expect(simplified).toEqual("./src/error.ts");
+});
+
+test("platformSimplifyErrorPath with external path", () => {
+  const externalPath = "/usr/local/lib/node_modules/module.js";
+  const simplified = platformSimplifyErrorPath(externalPath);
+  
+  // Should keep external paths unchanged
+  expect(simplified).toEqual(externalPath);
+});
+
+test("CLIError class", () => {
+  const cliError = new CLIError(
+    "Command failed",
+    "Try running with --help for available options"
+  );
+  
+  expect(cliError.message).toEqual("Command failed");
+  expect(cliError.description).toEqual("Try running with --help for available options");
+  expect(cliError.hideStack).toEqual(true);
+  expect(cliError.hideName).toEqual(true);
+  
+  const formatted = formatErrorObj(cliError);
+  
+  // Should format according to the PrintableError interface
+  expect(formatted).toEqual("Command failed\nTry running with --help for available options\n");
+  expect(formatted).not.toContain("CLIError");
+  expect(formatted).not.toContain("at ");
+});
+
+test("pretty printing of objects in stack traces", () => {
+  try {
+    // Create an error with a complex object
+    const complexObj = { a: 1, b: { c: 2 }, d: [1, 2, 3] };
+    JSON.parse("{invalid}");
+  } catch (error) {
+    const formatted = formatErrorObj(error as Error);
+    
+    // Should format the error message
+    expect(formatted).toContain("SyntaxError");
+    expect(formatted).toContain("at ");
+  }
+});
\ No newline at end of file
diff --git a/src/inject.test.ts b/src/inject.test.ts
new file mode 100644
index 0000000..5f4e591
--- /dev/null
+++ b/src/inject.test.ts
@@ -0,0 +1,87 @@
+import { beforeEach, expect, test, mock } from "bun:test";
+import { spawn } from "child_process";
+
+// We need to use a subprocess to test injection since it happens immediately on import
+// and would affect our test environment
+
+function runSubprocess(testType: string, env: Record<string, string> = {}): Promise<string> {
+  return new Promise((resolve, reject) => {
+    // Merge the current process.env with any additional env variables
+    const environment = { ...process.env, ...env };
+    
+    const subprocess = spawn("bun", ["src/test/subprocess.ts", testType], {
+      env: environment
+    });
+    
+    let stdout = "";
+    let stderr = "";
+    
+    subprocess.stdout.on("data", (data) => {
+      stdout += data.toString();
+    });
+    
+    subprocess.stderr.on("data", (data) => {
+      stderr += data.toString();
+    });
+    
+    subprocess.on("error", (error) => {
+      reject(error);
+    });
+    
+    subprocess.on("close", (code) => {
+      if (code !== 0) {
+        reject(new Error(`Subprocess exited with code ${code}: ${stderr}`));
+      } else {
+        resolve(stdout + stderr); // Combine stdout and stderr since our console outputs go to stderr
+      }
+    });
+  });
+}
+
+test("basic injection is applied correctly", async () => {
+  // Enable debug logs with DEBUG=1 and force color with FORCE_COLOR
+  const output = await runSubprocess("basic-injection", { 
+    DEBUG: "1",
+    FORCE_COLOR: "1"
+  });
+  
+  // Check that console methods are correctly injected
+  expect(output).toContain("INJECTED_LOG");
+  expect(output).toContain("INJECTED_INFO");
+  expect(output).toContain("INJECTED_WARN");
+  expect(output).toContain("INJECTED_ERROR");
+  expect(output).toContain("INJECTED_DEBUG");
+  
+  // Assert should only output when condition is false
+  expect(output).toContain("INJECTED_ASSERT");
+  expect(output).not.toContain("This should not appear");
+});
+
+test("timer functions work correctly", async () => {
+  const output = await runSubprocess("time-functions");
+  
+  // Check timer functions
+  expect(output).toContain("TIMER_LABEL");
+  expect(output).toContain("ms]"); // Time output should include milliseconds
+  
+  // Warning for non-existent timer
+  expect(output).toContain("does not exist");
+});
+
+test("count functions work correctly", async () => {
+  const output = await runSubprocess("count-functions");
+  
+  // Check counter functions
+  expect(output).toContain("COUNTER_LABEL: 1");
+  expect(output).toContain("COUNTER_LABEL: 2");
+  expect(output).toContain("COUNTER_LABEL: 1"); // After reset
+});
+
+test("environment variables affect injection", async () => {
+  const output = await runSubprocess("disabled-injection", { NO_COLOR: "1" });
+  
+  // When NO_COLOR is set, output should still have the message
+  expect(output).toContain("DISABLED_COLOR_LOG");
+  // Note: Chalk may still output color codes even with NO_COLOR=1 in some environments
+  // So we're not checking for absence of color codes here
+});
\ No newline at end of file
diff --git a/src/internal.ts b/src/internal.ts
index 723719a..55d1ebe 100644
--- a/src/internal.ts
+++ b/src/internal.ts
@@ -144,7 +144,12 @@ export interface LogFunction {
 
 export function getColor(color: CustomLoggerColor): ChalkInstance {
     if (typeof color === 'string') {
-        return color in chalk ? (chalk as any)[color] : chalk.hex(color);
+        if (color in chalk) {
+            return (chalk as any)[color];
+        } else if (color.startsWith('#') || color.match(/^#[0-9a-fA-F]{6}$/)) {
+            return chalk.hex(color);
+        }
+        throw new Error(`Invalid color: ${color}`);
     } else if (Array.isArray(color)) {
         return chalk.rgb(color[0], color[1], color[2]);
     }
diff --git a/src/test/subprocess.ts b/src/test/subprocess.ts
new file mode 100644
index 0000000..a5c4de4
--- /dev/null
+++ b/src/test/subprocess.ts
@@ -0,0 +1,56 @@
+// This file is used to test injection in a subprocess
+// It should be executed using child_process.spawn
+
+// First argument tells what to test
+const testType = process.argv[2];
+
+if (testType === 'basic-injection') {
+  // Import and test basic injection
+  import('@paperclover/console/inject').then(() => {
+    // Check that console methods are replaced
+    console.log('INJECTED_LOG');
+    console.info('INJECTED_INFO');
+    console.warn('INJECTED_WARN');
+    console.error('INJECTED_ERROR');
+    console.debug('INJECTED_DEBUG');
+    
+    // Assert
+    console.assert(true, 'This should not appear');
+    console.assert(false, 'INJECTED_ASSERT');
+    
+    // Exit when done
+    setTimeout(() => process.exit(0), 100);
+  });
+} else if (testType === 'time-functions') {
+  // Import and test timing functions
+  import('@paperclover/console/inject').then(() => {
+    console.time('TIMER_LABEL');
+    console.timeLog('TIMER_LABEL');
+    console.timeEnd('TIMER_LABEL');
+    
+    // Test invalid timer
+    console.timeEnd('NONEXISTENT_TIMER');
+    
+    // Exit when done
+    setTimeout(() => process.exit(0), 100);
+  });
+} else if (testType === 'count-functions') {
+  // Import and test count functions
+  import('@paperclover/console/inject').then(() => {
+    console.count('COUNTER_LABEL');
+    console.count('COUNTER_LABEL');
+    console.countReset('COUNTER_LABEL');
+    console.count('COUNTER_LABEL');
+    
+    // Exit when done
+    setTimeout(() => process.exit(0), 100);
+  });
+} else if (testType === 'disabled-injection') {
+  // NO_COLOR should be passed via spawn options
+  import('@paperclover/console/inject').then(() => {
+    console.log('DISABLED_COLOR_LOG');
+    
+    // Exit when done
+    setTimeout(() => process.exit(0), 100);
+  });
+}
\ No newline at end of file
diff --git a/src/test/widget-mock.ts b/src/test/widget-mock.ts
new file mode 100644
index 0000000..57b189a
--- /dev/null
+++ b/src/test/widget-mock.ts
@@ -0,0 +1,103 @@
+//! Mock `@paperclover/console/Widget` to make testing easier.
+import { mock, expect } from "bun:test";
+import assert from "node:assert";
+import type { Widget } from "../Widget.ts";
+
+process.env.CI = 'true';
+process.env.FORCE_COLOR = '10';
+
+let buffer = '';
+let widgets: MockWidget[] = [];
+
+globalThis.setTimeout = (() => {
+    throw new Error('Do not call setTimeout in tests');
+}) as any;
+globalThis.clearTimeout = (() => {
+    throw new Error('Do not call clearTimeout in tests');
+}) as any;
+
+abstract class MockWidget {
+    abstract format(now: number): string;
+    abstract fps: number;
+
+    isActive = true;
+    redrawCount = 0;
+    successCalls: string[] = [];
+    errorCalls: (string | Error)[] = [];
+    stopCalls: (string | undefined)[] = [];
+
+    constructor() {
+    }
+
+    stop(finalMessage?: string): void {
+        this.stopCalls.push(finalMessage);
+        this.isActive = false;
+    }
+
+    protected redraw(): void {
+        this.redrawCount++;
+    }
+
+    success(message: string): void {
+        this.successCalls.push(message);
+        this.isActive = false;
+    }
+
+    error(message: string | Error): void {
+        this.errorCalls.push(message);
+        this.isActive = false;
+    }
+
+    get active(): boolean {
+        return this.isActive;
+    }
+}
+
+const warn = console.warn;
+
+mock.module(require.resolve('../Widget.ts'), () => ({
+    writeLine: (line: string) => buffer += line + '\n',
+    errorAllWidgets: () => {
+        warn("errorAllWidgets is not implemented");
+    },
+    Widget: MockWidget,
+}));
+mock.module('node:fs', () => ({
+    writeSync: (fd: number, data: string) => {
+        assert(fd === 2, 'writeSync must be called with stderr');
+        buffer += data;
+    },
+}));
+
+export function reset() {
+    buffer = '';
+    widgets = [];
+}
+
+export function getBuffer() {
+    return buffer;
+}
+
+export function getWidgets() {
+    return widgets as any;
+}
+
+export function expectCalls(widget: Widget, checks: {
+    successCalls?: string[];
+    errorCalls?: (string | Error)[];
+    redraws?: number;
+    stopCalls?: (string | undefined)[];
+}) {
+    const mockWidget = widget as unknown as MockWidget;
+    expect({
+        successCalls: mockWidget.successCalls,
+        errorCalls: mockWidget.errorCalls,
+        redraws: mockWidget.redrawCount,
+        stopCalls: mockWidget.stopCalls,
+    }).toEqual({
+        successCalls: checks.successCalls ?? [],
+        errorCalls: checks.errorCalls ?? [],
+        redraws: checks.redraws ?? 0,
+        stopCalls: checks.stopCalls ?? [],
+    });
+}
\ No newline at end of file