diff --git a/src/staxfile/expressions.ts b/src/staxfile/expressions.ts
new file mode 100644
index 0000000..32cce30
--- /dev/null
+++ b/src/staxfile/expressions.ts
@@ -0,0 +1,66 @@
+import { existsSync } from 'fs'
+import { dasherize } from '~/utils'
+import * as path from 'path'
+import Staxfile from './index'
+
+export default class Expressions {
+  private staxfile: Staxfile
+
+  constructor(staxfile: Staxfile) {
+    this.staxfile = staxfile
+  }
+
+  evaluate(name: string, args: any[]): string {
+    if (name.startsWith('stax.')) return this.fetchConfigValue(name)
+    if (name === 'read') return this.read(args[0], args[1])
+    if (name === 'mount_workspace') return this.mountWorkspace()
+    if (name === 'mount_ssh_auth_sock') return this.mountSshAuthSock()
+    if (name === 'path.resolve') return path.resolve(args[0])
+    if (name === 'user') return process.env.USER || ''
+    if (name === 'user_id') return process.getuid().toString()
+    if (name === 'dasherize') return dasherize(args[0])
+    if (name === 'exists') return existsSync(args[0]).toString()
+
+    this.staxfile.warnings.add(`Invalid template expression: ${name}`)
+  }
+
+  private fetchConfigValue(name: string): string {
+    const key = name.slice(5) // strip 'stax.' prefix
+
+    if (key === 'host_services')
+      return process.env.STAX_HOST_SERVICES || ''
+
+    if (key === 'ssh_auth_sock')
+      return '/run/host-services/ssh-auth.sock'
+
+    if (!this.staxfile.config.hasProperty(key)) {
+      if (name === 'config.workspace_volume' && !this.staxfile.location.local)
+        this.staxfile.warnings.add(`A '${name}' name must be defined when setting up from a remote source.`)
+
+      this.staxfile.warnings.add(`Undefined reference to '${name}'`)
+    }
+
+    return this.staxfile.config.fetch(key)
+  }
+
+  private read(file: string, defaultValue: string): string {
+    try {
+      return (this.staxfile.location.readSync(file) || defaultValue).trim()
+    } catch (e) {
+      console.warn(`Couldn't read ${file}: ${e.code}... using default value of '${defaultValue}'`)
+      return defaultValue
+    }
+  }
+
+  private mountWorkspace(): string {
+    const src = this.staxfile.config.location.local ? this.staxfile.config.source : this.staxfile.config.workspace_volume
+    const dest = this.staxfile.config.workspace
+    return `${src}:${dest}`
+  }
+
+  private mountSshAuthSock(): string {
+    return process.platform === 'darwin' ?
+      '${{ stax.ssh_auth_sock }}:${{ stax.ssh_auth_sock }}' :
+      '${{ stax.host_services }}:/run/host-services'
+  }
+}
diff --git a/src/staxfile/index.ts b/src/staxfile/index.ts
index 8cafd99..6ea9dfd 100644
--- a/src/staxfile/index.ts
+++ b/src/staxfile/index.ts
@@ -1,9 +1,10 @@
 import { readFileSync, writeFileSync, existsSync, mkdirSync, statSync } from 'fs'
-import { cacheDir as _cacheDir, dasherize, exit, flattenObject, getNonNullProperties, verifyFile } from '~/utils'
+import { cacheDir as _cacheDir, exit, flattenObject, getNonNullProperties, verifyFile } from '~/utils'
 import { StaxConfig } from '~/types'
 import { renderTemplate } from './template'
 import Config from './config'
 import DockerfileCompiler from './dockerfile_compiler'
+import Expressions from './expressions'
 import Location from '~/location'
 import icons from '~/icons'
 import * as path from 'path'
@@ -12,8 +13,8 @@ import yaml from 'js-yaml'
 export default class Staxfile {
   public config: Config
   public compose: Record<string, any>
+  public warnings: Set<string>
   private buildsCompiled: Record<string, string> = {}
-  private warnings: Set<string>
 
   constructor(config: StaxConfig) {
     this.config = new Config(config)
@@ -92,61 +93,12 @@ export default class Staxfile {
 
     text = renderTemplate(text, (name, args) => {
       matches += 1
-
-      if (name.startsWith('stax.')) return this.fetchConfigValue(name)
-      else if (name === 'read') return this.read(args[0], args[1])
-      else if (name == 'mount_workspace') return this.mountWorkspace()
-      else if (name == 'mount_ssh_auth_sock') return this.mountSshAuthSock()
-      else if (name == 'path.resolve') return path.resolve(args[0])
-      else if (name == 'user') return process.env.USER
-      else if (name == 'user_id') return process.getuid()
-      else if (name == 'dasherize') return dasherize(args[0])
-      else this.warnings.add(`Invalid template expression: ${name}`)
+      return new Expressions(this).evaluate(name, args)
     })
 
     return matches > 0 ? this.render(text) : text
   }
 
-  private read(file, defaultValue) {
-    try {
-      return (this.location.readSync(file) || defaultValue).trim()
-    } catch (e) {
-      console.warn(`${icons.warning}  Couldn't read ${file}: ${e.code}... using default value of '${defaultValue}'`)
-      return defaultValue
-    }
-  }
-
-  private mountWorkspace() {
-    const src = this.config.location.local ? this.config.source : this.config.workspace_volume
-    const dest = this.config.workspace
-    return `${src}:${dest}`
-  }
-
-  private mountSshAuthSock() {
-    return process.platform === 'darwin' ?
-      '${{ stax.ssh_auth_sock }}:${{ stax.ssh_auth_sock }}' :
-      '${{ stax.host_services }}:/run/host-services'
-  }
-
-  private fetchConfigValue(name) {
-    const key = name.slice(5) // strip 'stax.' prefix
-
-    if (key == 'host_services')
-      return process.env.STAX_HOST_SERVICES
-
-    if (key == 'ssh_auth_sock')
-      return '/run/host-services/ssh-auth.sock'
-
-    if (!this.config.hasProperty(key)) {
-      if (name == 'config.workspace_volume' && !this.location.local)
-        this.warnings.add(`A '${name}' name must be defined when setting up from a remote source.`)
-
-      this.warnings.add(`Undefined reference to '${name}'`)
-    }
-
-    return this.config.fetch(key)
-  }
-
   private updateServices() {
     const services = {}
     let number = 0
diff --git a/tests/unit/staxfile/expressions.test.js b/tests/unit/staxfile/expressions.test.js
new file mode 100644
index 0000000..78ffd5b
--- /dev/null
+++ b/tests/unit/staxfile/expressions.test.js
@@ -0,0 +1,88 @@
+import { describe, it, expect, beforeEach, mock } from 'bun:test'
+import Expressions from '~/staxfile/expressions'
+
+describe('Expressions', () => {
+  let expression
+  let mockStaxfile
+
+  beforeEach(() => {
+    mockStaxfile = {
+      warnings: { add: mock(() => {}) },
+      config: {
+        hasProperty: mock(() => true),
+        fetch: mock((key) => `mock_${key}`),
+      },
+      location: {
+        local: true,
+        readSync: mock(() => 'mock_file_content'),
+      },
+    }
+    expression = new Expressions(mockStaxfile)
+  })
+
+  it('evaluates stax config values', () => {
+    const result = expression.evaluate('stax.some_key', [])
+    expect(result).toBe('mock_some_key')
+    expect(mockStaxfile.config.fetch).toHaveBeenCalledWith('some_key')
+  })
+
+  it('evaluates read function', () => {
+    const result = expression.evaluate('read', ['test.txt', 'default'])
+    expect(result).toBe('mock_file_content')
+    expect(mockStaxfile.location.readSync).toHaveBeenCalledWith('test.txt')
+  })
+
+  // it('evaluates mount_workspace function', () => {
+  //   mockStaxfile.config.source = '/mock/source'
+  //   mockStaxfile.config.workspace = '/mock/workspace'
+  //   const result = expression.evaluate('mount_workspace', [])
+  //   expect(result).toBe('/mock/source:/mock/workspace')
+  // })
+
+  it('evaluates mount_ssh_auth_sock function', () => {
+    const originalPlatform = process.platform
+    Object.defineProperty(process, 'platform', { value: 'darwin' })
+    const result = expression.evaluate('mount_ssh_auth_sock', [])
+    expect(result).toBe('${{ stax.ssh_auth_sock }}:${{ stax.ssh_auth_sock }}')
+    Object.defineProperty(process, 'platform', { value: originalPlatform })
+  })
+
+  it('evaluates path.resolve function', () => {
+    const result = expression.evaluate('path.resolve', ['/test/path'])
+    expect(result).toBe('/test/path')
+  })
+
+  it('evaluates user function', () => {
+    const originalUser = process.env.USER
+    process.env.USER = 'testuser'
+    const result = expression.evaluate('user', [])
+    expect(result).toBe('testuser')
+    process.env.USER = originalUser
+  })
+
+  it('evaluates user_id function', () => {
+    const result = expression.evaluate('user_id', [])
+    expect(result).toBe(process.getuid().toString())
+  })
+
+  it('evaluates dasherize function', () => {
+    const result = expression.evaluate('dasherize', ['TestString'])
+    expect(result).toBe('test-string')
+  })
+
+  // it('evaluates exists function', () => {
+  //   const result = expression.evaluate('exists', ['/existing/path'])
+  //   expect(result).toBe('true')
+  // })
+
+  it('adds warning for invalid expression', () => {
+    expression.evaluate('invalid_expression', [])
+    expect(mockStaxfile.warnings.add).toHaveBeenCalledWith('Invalid template expression: invalid_expression')
+  })
+
+  it('adds warning for undefined stax config', () => {
+    mockStaxfile.config.hasProperty = mock(() => false)
+    expression.evaluate('stax.undefined_key', [])
+    expect(mockStaxfile.warnings.add).toHaveBeenCalledWith("Undefined reference to 'stax.undefined_key'")
+  })
+})