docs: getting-started + codegen notebook --demo (#173)

# Motivation
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# Content
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# Testing
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# Please check the following before marking your PR as ready for review

- [ ] I have added tests for my changes
- [ ] I have updated the documentation or added new documentation as
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- [ ] I have read and agree to the [Contributor License
Agreement](../CLA.md)

---------

Co-authored-by: codegen-bot <team+codegenbot@codegen.sh>

Author: jayhack

docs/introduction/getting-started.mdx

@@ -9,7 +9,7 @@ A quick tour of Codegen in a Jupyter notebook.
 
 ## Installation
 
-Install [`codegen` on pypi](https://pypi.org/project/codegen/) via [uv](https://github.com/astral-sh/uv):
+Install [codegen](https://pypi.org/project/codegen/) on Pypi via [uv](https://github.com/astral-sh/uv):
 
 ```bash
 uv tool install codegen
@@ -34,8 +34,8 @@ The [codgen notebook](/cli/notebook) command creates a virtual environment and o
 # Navigate to your repository
 cd path/to/git/repository
 
-# Initialize codegen and launch Jupyter
-codegen notebook
+# Initialize codegen and launch Jupyter with a demo notebook
+codegen notebook --demo
 ```
 
 This will:
@@ -47,7 +47,7 @@ This will:
 2. Launch Jupyter Lab with a pre-configured notebook
 
 <Tip>
-  The notebook comes pre-configured to load your codebase, so you can start
+  The `notebook --demo` comes pre-configured to load [FastAPI](https://github.com/fastapi/fastapi)'s codebase , so you can start
   exploring right away!
 </Tip>
 
@@ -58,13 +58,17 @@ Instantiating a [Codebase](/api-reference/core/Codebase) will automatically pars
 ```python
 from codegen import Codebase
 
-# Parse a codebase
-codebase = Codebase("./")
+# Initialize FastAPI codebase
+print('Cloning and parsing FastAPI to /tmp/codegen/fastapi...')
+codebase = Codebase.from_repo('fastapi/fastapi')
+
+# To initialize an existing local codebase, use this constructor
+# codebase = Codebase("path/to/git/repo")
 ```
 
 <Note>
   This will automatically infer the programming language of the codebase and
-  parse all files in the codebase.
+  parse all files in the codebase. Learn more about [parsing codebases here](/building-with-codegen/parsing-codebases)
 </Note>
 
 <Tip>
@@ -81,8 +85,10 @@ Here are some common patterns for code navigation in Codegen:
 
 - Iterate over all [Functions](/api-reference/core/Function) with [Codebase.functions](/api-reference/core/Codebase#functions)
 - View class inheritance with [Class.superclasses](/api-reference/core/Class#superclasses)
-- View function call-sites with [Function.call_sites](/api-reference/core/Function#call-sites)
 - View function usages with [Function.usages](/api-reference/core/Function#usages)
+- View inheritance hierarchies with [inheritance APIs](https://docs.codegen.com/building-with-codegen/class-api#working-with-inheritance)
+- Identify recursive functions by looking at [FunctionCalls](https://docs.codegen.com/building-with-codegen/function-calls-and-callsites)
+- View function call-sites with [Function.call_sites](/api-reference/core/Function#call-sites)
 
 ```python
 # Print overall stats
@@ -108,7 +114,7 @@ if recursive:
         print(f"  - {func.name}")
 ```
 
-### Analyzing Tests
+## Analyzing Tests
 
 Let's specifically drill into large test files, which can be cumbersome to manage.
 
@@ -135,38 +141,52 @@ for file, num_tests in file_test_counts.most_common()[:5]:
     print(f"   💡 Functions: {len(file.functions)}")
 ```
 
-### Splitting Up Large Test Files
+## Splitting Up Large Test Files
+
+Lets split up the largest test files into separate modules for better organization.
+
+This uses Codegen's [codebase.move_to_file(...)](/building-with-codegen/moving-symbols), which will:
+- update all imports
+- (optionally) move dependencies
+- do so very fast ⚡️
 
-Lets split up the largest test files into separate modules for better organization:
+While maintaining correctness.
 
 ```python
-print("\n📦 Splitting Test Files")
+filename = 'tests/test_path.py'
+print(f"📦 Splitting Test File: {filename}")
 print("=" * 50)
 
-# Process top 5 largest test files
-for file, num_tests in file_test_counts.most_common()[:5]:
-    # Create a new directory based on the file name
-    base_name = file.path.replace('.py', '')
-    print(f"\n🔄 Processing: {file.filepath}")
-    print(f"   📊 {num_tests} test classes to split")
-
-    # Move each test class to its own file
-    for test_class in file.classes:
-        if test_class.name.startswith('Test'):
-            # Create descriptive filename from test class name
-            new_file = f"{base_name}/{test_class.name.lower()}.py"
-            print(f"   📝 Moving {test_class.name} -> {new_file}")
-
-            # Codegen handles all the complexity:
-            # - Creates directories if needed
-            # - Updates all imports automatically
-            # - Maintains test dependencies
-            # - Preserves decorators and docstrings
-            test_class.move_to_file(new_file)
+# Grab a file
+file = codebase.get_file(filename)
+base_name = filename.replace('.py', '')
+
+# Group tests by subpath
+test_groups = {}
+for test_function in file.functions:
+    if test_function.name.startswith('test_'):
+        test_subpath = '_'.join(test_function.name.split('_')[:3])
+        if test_subpath not in test_groups:
+            test_groups[test_subpath] = []
+        test_groups[test_subpath].append(test_function)
+
+# Print and process each group
+for subpath, tests in test_groups.items():
+    print(f"\\n{subpath}/")
+    new_filename = f"{base_name}/{subpath}.py"
+
+    # Create file if it doesn't exist
+    if not codebase.has_file(new_filename):
+        new_file = codebase.create_file(new_filename)
+    file = codebase.get_file(new_filename)
+
+    # Move each test in the group
+    for test_function in tests:
+        print(f"    - {test_function.name}")
+        test_function.move_to_file(new_file, strategy="add_back_edge")
 
 # Commit changes to disk
 codebase.commit()
-
 ```
 
 <Warning>
@@ -299,14 +319,15 @@ if base_class:
     Understand key concepts like working with files, functions, imports, and the
     call graph to effectively manipulate code.
   </Card>
+  <Card title="IDE Setup" icon="window" href="/introduction/ide-usage">
+    Iterate locally with your favorite IDE, work with a debugger and build sophisticated codemods
+  </Card>
   <Card
     title="Integrate with AI Tools"
-    icon="robot"
+    icon="microchip"
     href="/introduction/work-with-ai"
   >
     Learn how to use Codegen with Cursor, Devin, Windsurf, and more.
   </Card>
-  <Card title="API Reference" icon="code" href="/api-reference">
-    Explore the complete API documentation for all Codegen classes and methods.
-  </Card>
+
 </CardGroup>

src/codegen/cli/commands/notebook/main.py

@@ -20,17 +20,19 @@ def create_jupyter_dir() -> Path:
 
 
 @click.command(name="notebook")
+@click.option("--background", is_flag=True, help="Run Jupyter Lab in the background")
+@click.option("--demo", is_flag=True, help="Create a demo notebook with FastAPI example code")
 @requires_init
-def notebook_command(session: CodegenSession):
-    """Open a Jupyter notebook with the current codebase loaded."""
+def notebook_command(session: CodegenSession, background: bool, demo: bool):
+    """Launch Jupyter Lab with a pre-configured notebook for exploring your codebase."""
     with create_spinner("Setting up Jupyter environment...") as status:
         venv = VenvManager()
 
         status.update("Checking Jupyter installation...")
         venv.ensure_jupyter()
 
         jupyter_dir = create_jupyter_dir()
-        notebook_path = create_notebook(jupyter_dir)
+        notebook_path = create_notebook(jupyter_dir, demo=demo)
 
         status.update("Running Jupyter Lab...")