diff --git a/ofborg/src/nix.rs b/ofborg/src/nix.rs
index dbb21c2..5692a28 100644
--- a/ofborg/src/nix.rs
+++ b/ofborg/src/nix.rs
@@ -31,6 +31,12 @@ impl Nix {
     }
 
     pub fn safely_build_attrs(&self, nixpkgs: &Path, file: &str, attrs: Vec<String>) -> Result<File,File> {
+        let cmd = self.safely_build_attrs_cmd(nixpkgs, file, attrs);
+
+        return self.run(cmd, true);
+    }
+
+    pub fn safely_build_attrs_cmd(&self, nixpkgs: &Path, file: &str, attrs: Vec<String>) -> Command {
         let mut attrargs: Vec<String> = Vec::with_capacity(3 + (attrs.len() * 2));
         attrargs.push(file.to_owned());
         attrargs.push(String::from("--no-out-link"));
@@ -40,14 +46,14 @@ impl Nix {
             attrargs.push(attr);
         }
 
-        return self.safely("nix-build", nixpkgs, attrargs, true);
+        return self.safe_command("nix-build", nixpkgs, attrargs);
     }
 
     pub fn safely(&self, cmd: &str, nixpkgs: &Path, args: Vec<String>, keep_stdout: bool) -> Result<File,File> {
-        let mut nixpath = OsString::new();
-        nixpath.push("nixpkgs=");
-        nixpath.push(nixpkgs.as_os_str());
+        return self.run(self.safe_command(cmd, nixpkgs, args), keep_stdout);
+    }
 
+    pub fn run(&self, mut cmd: Command, keep_stdout: bool) -> Result<File,File> {
         let stderr = tempfile().expect("Fetching a stderr tempfile");
         let mut reader = stderr.try_clone().expect("Cloning stderr to the reader");
 
@@ -60,22 +66,11 @@ impl Nix {
             stdout = Stdio::null();
         }
 
-
-        let status = Command::new(cmd)
-            .env_clear()
-            .current_dir(nixpkgs)
+        let status = cmd
             .stdout(Stdio::from(stdout))
             .stderr(Stdio::from(stderr))
-            .env("HOME", "/homeless-shelter")
-            .env("NIX_PATH", nixpath)
-            .env("NIX_REMOTE", &self.remote)
-            .args(&["--show-trace"])
-            .args(&["--option", "restrict-eval", "true"])
-            .args(&["--option", "build-timeout", &format!("{}", self.build_timeout)])
-            .args(&["--argstr", "system", &self.system])
-            .args(args)
             .status()
-            .expect(format!("Running {:?}", cmd).as_ref());
+            .expect(format!("Running a program ...").as_ref());
 
         reader.seek(SeekFrom::Start(0)).expect("Seeking to Start(0)");
 
@@ -85,4 +80,217 @@ impl Nix {
             return Err(reader)
         }
     }
+
+    pub fn safe_command(&self, cmd: &str, nixpkgs: &Path, args: Vec<String>) -> Command {
+        let mut nixpath = OsString::new();
+        nixpath.push("nixpkgs=");
+        nixpath.push(nixpkgs.as_os_str());
+
+        let mut command = Command::new(cmd);
+        command.env_clear();
+        command.current_dir(nixpkgs);
+        command.env("HOME", "/homeless-shelter");
+        command.env("NIX_PATH", nixpath);
+        command.env("NIX_REMOTE", &self.remote);
+        command.args(&["--show-trace"]);
+        command.args(&["--option", "restrict-eval", "true"]);
+        command.args(&["--option", "build-timeout", &format!("{}", self.build_timeout)]);
+        command.args(&["--argstr", "system", &self.system]);
+        command.args(args);
+
+        return command;
+    }
+
+}
+
+#[cfg(test)]
+mod tests {
+    fn nix() -> Nix {
+        Nix::new("x86_64-linux".to_owned(), "daemon".to_owned(), 1800)
+    }
+
+    fn build_path() -> PathBuf {
+        let mut cwd = env::current_dir().unwrap();
+        cwd.push(Path::new("./test-srcs/build"));
+        return cwd;
+    }
+
+    fn passing_eval_path() -> PathBuf {
+        let mut cwd = env::current_dir().unwrap();
+        cwd.push(Path::new("./test-srcs/eval"));
+        return cwd;
+    }
+
+    #[derive(Debug)]
+    enum Expect {
+        Pass,
+        Fail,
+    }
+
+    fn assert_run(res: Result<File,File>, expected: Expect, require: Vec<&str>) {
+        let expectation_held: bool = match expected {
+            Expect::Pass => res.is_ok(),
+            Expect::Fail => res.is_err(),
+        };
+
+        let file: File = match res {
+            Ok(file) => file,
+            Err(file) => file,
+        };
+
+        let lines: Vec<String> = BufReader::new(file)
+            .lines()
+            .into_iter()
+            .filter(|line| line.is_ok())
+            .map(|line| line.unwrap())
+            .collect();
+
+        let buildlog = lines
+            .into_iter()
+            .map(|line| format!("   | {}", line))
+            .collect::<Vec<String>>()
+            .join("\n");
+
+        let total_requirements = require.len();
+        let mut missed_requirements: usize = 0;
+        let requirements_held: Vec<Result<String, String>> =
+            require.into_iter()
+            .map(|line| line.to_owned())
+            .map(|line|
+                 if buildlog.contains(&line) {
+                     Ok(line)
+                 } else {
+                     missed_requirements += 1;
+                     Err(line)
+                 }
+            )
+            .collect();
+
+        let mut prefixes: Vec<String> = vec![
+            "".to_owned(),
+            "".to_owned(),
+        ];
+
+        if !expectation_held {
+            prefixes.push(format!(
+                "The run was expected to {:?}, but did not.",
+                expected
+            ));
+            prefixes.push("".to_owned());
+        } else {
+            prefixes.push(format!(
+                "The run was expected to {:?}, and did.",
+                expected
+            ));
+            prefixes.push("".to_owned());
+        }
+
+        let mut suffixes = vec![
+            "".to_owned(),
+            format!("{} out of {} required lines matched.",
+                    (total_requirements - missed_requirements),
+                    total_requirements
+            ),
+            "".to_owned(),
+        ];
+
+        for expected_line in requirements_held {
+            suffixes.push(format!(" - {:?}", expected_line));
+        }
+        suffixes.push("".to_owned());
+
+        let output_blocks: Vec<Vec<String>> = vec![
+            prefixes,
+            vec![buildlog, "".to_owned()],
+            suffixes,
+        ];
+
+        let output_blocks_strings: Vec<String> =
+            output_blocks
+            .into_iter()
+            .map(|lines| lines.join("\n"))
+            .collect();
+
+        let output: String = output_blocks_strings
+            .join("\n");
+
+        if expectation_held && missed_requirements == 0 {
+        } else {
+            panic!(output);
+        }
+    }
+
+    use super::*;
+    use std::io::BufReader;
+    use std::io::BufRead;
+    use std::path::PathBuf;
+    use std::env;
+
+    #[test]
+    fn safely_build_attrs_success() {
+        let nix = nix();
+
+        let ret: Result<File,File>  = nix.safely_build_attrs(
+            build_path().as_path(),
+            "default.nix",
+            vec![String::from("success")]
+        );
+
+        assert_run(ret, Expect::Pass, vec![
+            "-success.drv",
+            "building path(s)",
+            "hi",
+            "-success"
+        ]);
+    }
+
+    #[test]
+    fn safely_build_attrs_failure() {
+        let nix = nix();
+
+        let ret: Result<File,File>  = nix.safely_build_attrs(
+            build_path().as_path(),
+            "default.nix",
+            vec![String::from("failed")]
+        );
+
+        assert_run(ret, Expect::Fail, vec![
+            "-failed.drv",
+            "building path(s)",
+            "hi",
+            "failed to produce output path"
+        ]);
+    }
+
+    #[test]
+    fn strict_sandboxing() {
+        let ret: Result<File,File>  = nix().safely_build_attrs(
+            build_path().as_path(),
+            "default.nix",
+            vec![String::from("sandbox-violation")]
+        );
+
+        assert_run(ret, Expect::Fail, vec![
+            "error: while evaluating the attribute",
+            "access to path",
+            "is forbidden in restricted mode"
+        ]);
+    }
+
+
+    #[test]
+    fn instantiation() {
+        let ret: Result<File,File>  = nix().safely(
+            "nix-instantiate",
+            passing_eval_path().as_path(),
+            vec![],
+            true
+        );
+
+        assert_run(ret, Expect::Pass, vec![
+            "the result might be removed by the garbage collector",
+            "-failed.drv",
+            "-success.drv"
+        ]);
+    }
 }
diff --git a/ofborg/test-srcs/build/default.nix b/ofborg/test-srcs/build/default.nix
new file mode 100644
index 0000000..840aa12
--- /dev/null
+++ b/ofborg/test-srcs/build/default.nix
@@ -0,0 +1,27 @@
+let
+  nix = import <nix/config.nix>;
+in {
+  success = derivation {
+    name = "success";
+    system = builtins.currentSystem;
+    builder = nix.shell;
+    args = [
+      "-c"
+      "echo hi; echo ${toString builtins.currentTime} > $out" ];
+  };
+
+  failed = derivation {
+    name = "failed";
+    system = builtins.currentSystem;
+    builder = nix.shell;
+    args = [
+      "-c"
+      "echo hi; echo ${toString builtins.currentTime}" ];
+  };
+
+  sandbox-violation = derivation {
+    name = "sandbox-violation";
+    system = builtins.currentSystem;
+    builder = ./../../src;
+  };
+}
diff --git a/ofborg/test-srcs/build/succeed.sh b/ofborg/test-srcs/build/succeed.sh
new file mode 100644
index 0000000..7ec52d0
--- /dev/null
+++ b/ofborg/test-srcs/build/succeed.sh
@@ -0,0 +1,4 @@
+#!/bin/sh
+
+echo "$@"
+echo hi
diff --git a/ofborg/test-srcs/eval/default.nix b/ofborg/test-srcs/eval/default.nix
new file mode 100644
index 0000000..35981f7
--- /dev/null
+++ b/ofborg/test-srcs/eval/default.nix
@@ -0,0 +1,21 @@
+let
+  nix = import <nix/config.nix>;
+in rec {
+  success = derivation {
+    name = "success";
+    system = builtins.currentSystem;
+    builder = nix.shell;
+    args = [
+      "-c"
+      "echo hi; echo ${toString builtins.currentTime} > $out" ];
+  };
+
+  failed = derivation {
+    name = "failed";
+    system = builtins.currentSystem;
+    builder = nix.shell;
+    args = [
+      "-c"
+      "echo hi; echo ${toString builtins.currentTime}; echo ${success}" ];
+  };
+}