diff --git a/Cargo.toml b/Cargo.toml
index 2da5efc..3374c2d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -17,7 +17,7 @@ name = "bonsai"
 doc = false
 
 [dependencies]
-oak = "^0.5.3"
+oak = "^0.5.4"
 oak_runtime = "^0.5.5"
 partial = "0.2.3"
 clap = "^2"
diff --git a/src/back/compiler/expression.rs b/src/back/compiler/expression.rs
index 93bf6d7..143ae9d 100644
--- a/src/back/compiler/expression.rs
+++ b/src/back/compiler/expression.rs
@@ -13,29 +13,32 @@
 // limitations under the License.
 
 use context::*;
+use session::*;
 use back::code_formatter::*;
 use std::collections::HashMap;
 
 /// Useful to compile expression without using the environment (for example when initializing a field).
 /// Precondition: All the free variables occuring in `expr` are supposed to be in scope.
-pub fn compile_expression(context: &Context, fmt: &mut CodeFormatter, expr: Expr) {
-  ExpressionCompiler::new(context, fmt).compile(expr)
+pub fn compile_expression(session: &Session, context: &Context, fmt: &mut CodeFormatter, expr: Expr) {
+  ExpressionCompiler::new(session, context, fmt).compile(expr)
 }
 
 /// Wrap the expression inside a closure `(env) -> [[expr]]` to be executed later with the environment.
-pub fn compile_closure(context: &Context, fmt: &mut CodeFormatter, expr: Expr, return_expr: bool) {
-  ExpressionCompiler::new(context, fmt).closure(expr, return_expr)
+pub fn compile_closure(session: &Session, context: &Context, fmt: &mut CodeFormatter, expr: Expr, return_expr: bool) {
+  ExpressionCompiler::new(session, context, fmt).closure(expr, return_expr)
 }
 
 struct ExpressionCompiler<'a> {
+  session: &'a Session,
   context: &'a Context,
   fmt: &'a mut CodeFormatter
 }
 
 impl<'a> ExpressionCompiler<'a>
 {
-  fn new(context: &'a Context, fmt: &'a mut CodeFormatter) -> Self {
+  fn new(session: &'a Session, context: &'a Context, fmt: &'a mut CodeFormatter) -> Self {
     ExpressionCompiler {
+      session: session,
       context: context,
       fmt: fmt
     }
diff --git a/src/back/compiler/module.rs b/src/back/compiler/module.rs
index 021a5f6..63c721e 100644
--- a/src/back/compiler/module.rs
+++ b/src/back/compiler/module.rs
@@ -13,23 +13,29 @@
 // limitations under the License.
 
 use context::*;
+use session::*;
 use back::code_formatter::*;
 use back::compiler::expression::*;
 use back::compiler::statement::*;
 
-pub fn compile_module(context: &Context, module: JModule) -> Partial<String> {
-  ModuleCompiler::new(context).compile(module)
+pub fn compile_module(env: Env<Context>, module: JModule) -> Env<(Context, String)> {
+  env.and_next(|session, context| {
+    let code = ModuleCompiler::new(&session, &context).compile(module);
+    Env::new(session, code.map(|code| (context, code)))
+  })
 }
 
 struct ModuleCompiler<'a> {
+  session: &'a Session,
   context: &'a Context,
   fmt: CodeFormatter
 }
 
 impl<'a> ModuleCompiler<'a>
 {
-  fn new(context: &'a Context) -> Self {
+  fn new(session: &'a Session, context: &'a Context) -> Self {
     ModuleCompiler {
+      session: session,
       context: context,
       fmt: CodeFormatter::new()
     }
@@ -70,9 +76,9 @@ impl<'a> ModuleCompiler<'a>
   }
 
   fn runtime_boilerplate(&mut self, module: &JModule) {
-    self.runtime_object_uid(&module);
-    self.runtime_init_method(&module);
-    self.runtime_destroy_method(&module);
+    self.runtime_object_uid(module);
+    self.runtime_init_method(module);
+    self.runtime_destroy_method(module);
   }
 
   fn class_decl(&mut self, jclass: &JClass) {
@@ -95,11 +101,11 @@ impl<'a> ModuleCompiler<'a>
   }
 
   fn main_method(&mut self, class_name: Ident) {
-    if let Some(main) = self.context.config().main_method.clone() {
+    if let Some(main) = self.session.config().main_method.clone() {
       if main.class == *class_name {
         self.fmt.push_line("public static void main(String[] args)");
         self.fmt.open_block();
-        let machine_method = if self.context.config().debug { "createDebug" } else { "create" };
+        let machine_method = if self.session.config().debug { "createDebug" } else { "create" };
         self.fmt.push_block(format!("\
           {} current = new {}();\n\
           Program program = current.{}();\n\
@@ -160,7 +166,7 @@ impl<'a> ModuleCompiler<'a>
         self.fmt.push(&format!("new {}()", field.binding.ty.name));
       }
       else {
-        compile_expression(&self.context, &mut self.fmt, expr);
+        compile_expression(self.session, self.context, &mut self.fmt, expr);
       }
     }
     self.fmt.terminate_line(";");
@@ -246,7 +252,7 @@ impl<'a> ModuleCompiler<'a>
     self.proc_uid(&process, proc_instance);
     self.fmt.push_line("return");
     self.fmt.indent();
-    compile_statement(self.context, &mut self.fmt, process.body);
+    compile_statement(self.session, self.context, &mut self.fmt, process.body);
     self.fmt.unindent();
     self.fmt.terminate_line(";");
     self.fmt.close_block();
diff --git a/src/driver/config.rs b/src/driver/config.rs
index 281ee68..7573696 100644
--- a/src/driver/config.rs
+++ b/src/driver/config.rs
@@ -96,7 +96,7 @@ impl Config
       output: file_to_test,
       libs: libs,
       main_method: None,
-      debug: true,
+      debug: false,
       testing_mode: true
     }
   }
diff --git a/src/driver/mod.rs b/src/driver/mod.rs
index f4e9c1a..6977e5b 100644
--- a/src/driver/mod.rs
+++ b/src/driver/mod.rs
@@ -22,7 +22,7 @@ use self::module_file::*;
 use session::*;
 use front;
 use middle;
-// use back;
+use back;
 use context::Context;
 use ast::{JModule, JCrate, TestAnnotation};
 
@@ -67,19 +67,18 @@ fn run_middle<'a>(env: Env<Context>) -> Env<Context> {
   middle::analyse_bonsai(env)
 }
 
-fn run_back(session: Session, context: Context) -> Env<Context> {
+pub fn run_back(session: Session, context: Context) -> Env<Context> {
   assert_eq!(session.has_errors(), false);
-  Env::value(session, context)
-  // context.ast.modules.clone()
-  //   .into_iter()
-  //   .filter(|module| module.file.is_lib())
-  //   .fold(Env::value(session, context), |env, module| {
-  //     let file = module.file.clone();
-  //     back::compile_module(env, module)
-  //       .map(|(context, output)| {
-  //         file.write_output(output);
-  //         context
-  //       })
-  //       .ensure(ABORT_MSG)
-  //   })
+  context.ast.modules.clone()
+    .into_iter()
+    .filter(|module| module.file.is_lib())
+    .fold(Env::value(session, context), |env, module| {
+      let file = module.file.clone();
+      back::compile_module(env, module)
+        .map(|(context, output)| {
+          file.write_output(output);
+          context
+        })
+        .ensure(ABORT_MSG)
+    })
 }
diff --git a/src/lib.rs b/src/lib.rs
index d69e739..6fbf301 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -30,4 +30,4 @@ pub mod context;
 pub mod driver;
 pub mod front;
 pub mod middle;
-// pub mod back;
+pub mod back;
diff --git a/src/main.rs b/src/main.rs
index f977a87..819b182 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -30,7 +30,7 @@ mod context;
 mod driver;
 mod front;
 mod middle;
-// mod back;
+mod back;
 
 fn main() {
   driver::run();
diff --git a/tests/test/unit.rs b/tests/test/compile_test.rs
similarity index 82%
rename from tests/test/unit.rs
rename to tests/test/compile_test.rs
index c56af9f..e24786c 100644
--- a/tests/test/unit.rs
+++ b/tests/test/compile_test.rs
@@ -19,14 +19,12 @@ use test::*;
 use libbonsai::ast::*;
 use libbonsai::context::*;
 
-use partial::*;
-
 use std::path::{PathBuf};
 
 use ExpectedResult::*;
 use ExpectedResult;
 
-pub struct Unit<'a>
+pub struct CompileTest<'a>
 {
   display: &'a mut Display,
   result: Partial<Context>,
@@ -36,7 +34,7 @@ pub struct Unit<'a>
   test_path: PathBuf
 }
 
-impl<'a> Unit<'a>
+impl<'a> CompileTest<'a>
 {
   pub fn new(display: &'a mut Display,
     result: Partial<Context>, expect: ExpectedResult,
@@ -44,7 +42,7 @@ impl<'a> Unit<'a>
     obtained_diagnostics: Vec<CompilerTest>,
     test_path: PathBuf) -> Self
   {
-    Unit {
+    CompileTest {
       display: display,
       result: result,
       expect: expect,
@@ -54,10 +52,21 @@ impl<'a> Unit<'a>
     }
   }
 
-  pub fn diagnostic(mut self) {
+  /// Returns the context if the compilation succeeded as expected.
+  pub fn diagnostic(mut self) -> Option<Context> {
     let file_name = self.file_name();
     if self.compilation_status(file_name.clone()) {
-      self.compare_diagnostics(file_name);
+      self.compare_diagnostics(file_name)
+    }
+    else {
+      None
+    }
+  }
+
+  pub fn context_to_option(self) -> Option<Context> {
+    match self.result {
+      Partial::Value(x) => Some(x),
+      _ => None
     }
   }
 
@@ -76,15 +85,17 @@ impl<'a> Unit<'a>
     }
   }
 
-  fn compare_diagnostics(self, file_name: String) {
+  fn compare_diagnostics(self, file_name: String) -> Option<Context> {
     if &self.obtained_diagnostics != &self.expected_diagnostics {
       self.display.diagnostics_failure(self.test_path, file_name,
         &self.obtained_diagnostics,
         &self.expected_diagnostics,
       );
+      None
     }
     else {
       self.display.success(file_name);
+      self.context_to_option()
     }
   }
 
diff --git a/tests/test/engine.rs b/tests/test/engine.rs
index 0510e87..945f6c3 100644
--- a/tests/test/engine.rs
+++ b/tests/test/engine.rs
@@ -14,6 +14,7 @@
 
 use libbonsai::session::*;
 use libbonsai::driver::*;
+use libbonsai::context::*;
 
 use syntex_syntax::codemap::{CodeMap};
 use std::rc::Rc;
@@ -21,7 +22,6 @@ use std::cell::RefCell;
 
 use std::path::{PathBuf, Path};
 use std::fs::read_dir;
-use partial::*;
 
 use test::*;
 use test::ExpectedResult::*;
@@ -63,14 +63,14 @@ impl Engine
   }
 
   fn test_directory(&mut self, start_msg: String, directory: PathBuf,
-    expect: ExpectedResult, run: bool)
+    expect: ExpectedResult, execute: bool)
   {
     self.display.info(start_msg);
     match read_dir(&directory) {
       Ok(dir_entries) => {
         for entry in dir_entries.map(Result::unwrap).map(|entry| entry.path()) {
           if entry.is_file() {
-            self.compile_and_run(entry, expect, run);
+            self.compile_and_run(entry, expect, execute);
           } else {
             self.display.warn(format!("Entry ignored because it's not a file."));
             self.display.path(entry);
@@ -83,7 +83,7 @@ impl Engine
     }
   }
 
-  fn compile_and_run(&mut self, filepath: PathBuf, expect: ExpectedResult, run: bool) {
+  fn compile_and_run(&mut self, filepath: PathBuf, expect: ExpectedResult, execute: bool) {
     let obtained_diagnostics = Rc::new(RefCell::new(vec![]));
     let codemap = Rc::new(CodeMap::new());
     let emitter = Box::new(TestEmitter::new(obtained_diagnostics.clone(), codemap.clone()));
@@ -93,11 +93,19 @@ impl Engine
     let session = session.reset_diagnostic();
     let obtained_diagnostics = Rc::try_unwrap(obtained_diagnostics)
       .expect("Could not extract `obtained_diagnostics`.").into_inner();
-    let unit = Unit::new(&mut self.display, context, expect, session.compiler_tests,
-      obtained_diagnostics, filepath);
-    unit.diagnostic();
+    let context = {
+      let compile_test = CompileTest::new(&mut self.display, context, expect, session.compiler_tests.clone(),
+        obtained_diagnostics, filepath);
+      compile_test.diagnostic()
+    };
+    if let Some(context) = context {
+      if execute {
+        self.run_file(session, context);
+      }
+    }
   }
 
-  fn run_file(&mut self, filepath: PathBuf) {
+  fn run_file(&mut self, session: Session, context: Context) {
+    run_back(session, context).expect("[Test] Could not generate the Bonsai code.");
   }
 }
diff --git a/tests/test/mod.rs b/tests/test/mod.rs
index 4bae516..2d83967 100644
--- a/tests/test/mod.rs
+++ b/tests/test/mod.rs
@@ -13,13 +13,13 @@
 // limitations under the License.
 
 pub mod display;
-pub mod unit;
+pub mod compile_test;
 pub mod expected_result;
 pub mod test_emitter;
 pub mod engine;
 
 pub use self::display::*;
-pub use self::unit::*;
+pub use self::compile_test::*;
 pub use self::expected_result::*;
 pub use self::test_emitter::*;
 pub use self::engine::*;