Add nix-shell support (#173)

tests/testsuite/main.rs

@@ -7,6 +7,7 @@ mod golang;
 mod jobs;
 mod line_break;
 mod modules;
+mod nix_shell;
 mod nodejs;
 mod python;
 mod ruby;

tests/testsuite/nix_shell.rs

@@ -0,0 +1,58 @@
+use ansi_term::Color;
+use std::io;
+
+use crate::common;
+
+#[test]
+fn no_env_variables() -> io::Result<()> {
+    let output = common::render_module("nix_shell").output()?;
+    let actual = String::from_utf8(output.stdout).unwrap();
+    assert_eq!("", actual);
+    Ok(())
+}
+
+#[test]
+fn invalid_env_variables() -> io::Result<()> {
+    let output = common::render_module("nix_shell")
+        .env("IN_NIX_SHELL", "something_wrong")
+        .output()?;
+    let actual = String::from_utf8(output.stdout).unwrap();
+    assert_eq!("", actual);
+    Ok(())
+}
+
+#[test]
+fn pure_shell() -> io::Result<()> {
+    let output = common::render_module("nix_shell")
+        .env("IN_NIX_SHELL", "pure")
+        .output()?;
+    let actual = String::from_utf8(output.stdout).unwrap();
+
+    let expected = format!("via {} ", Color::Red.bold().paint("pure"));
+    assert_eq!(expected, actual);
+    Ok(())
+}
+
+#[test]
+fn impure_shell() -> io::Result<()> {
+    let output = common::render_module("nix_shell")
+        .env("IN_NIX_SHELL", "impure")
+        .output()?;
+    let actual = String::from_utf8(output.stdout).unwrap();
+
+    let expected = format!("via {} ", Color::Red.bold().paint("impure"));
+    assert_eq!(expected, actual);
+    Ok(())
+}
+
+#[test]
+fn lorri_shell() -> io::Result<()> {
+    let output = common::render_module("nix_shell")
+        .env("IN_NIX_SHELL", "1")
+        .output()?;
+    let actual = String::from_utf8(output.stdout).unwrap();
+
+    let expected = format!("via {} ", Color::Red.bold().paint("impure"));
+    assert_eq!(expected, actual);
+    Ok(())
+}