feat: Add a disabled configuration option for modules (#86)

• Add support for the disabled configuration option
This will allow you to selectively disable modules that you don't want or need. 😄
• Overwrite starship configuration file path with STARSHIP_CONFIG environment variable
• Write tests for the two configuration options that are available

tests/testsuite/common.rs

@@ -1,15 +1,36 @@
+use lazy_static::lazy_static;
+use std::io::prelude::*;
+use std::path::{Path, PathBuf};
 use std::{io, process};
 
-pub fn render_prompt() -> process::Command {
+lazy_static! {
+    static ref MANIFEST_DIR: &'static Path = Path::new(env!("CARGO_MANIFEST_DIR"));
+    pub static ref FIXTURES_DIR: PathBuf = MANIFEST_DIR.join("tests/fixtures");
+    static ref EMPTY_CONFIG: PathBuf = MANIFEST_DIR.join("empty_config.toml");
+}
+
+/// Run an instance of starship
+fn run_starship() -> process::Command {
     let mut command = process::Command::new("./target/debug/starship");
-    command.arg("prompt");
+
+    command
+        .arg("prompt")
+        .env_clear()
+        .env("PATH", env!("PATH")) // Provide the $PATH variable so that external programs are runnable
+        .env("STARSHIP_CONFIG", EMPTY_CONFIG.as_os_str());
 
     command
 }
 
 pub fn render_module(module_name: &str) -> process::Command {
     let mut command = process::Command::new("./target/debug/starship");
-    command.arg("module").arg(module_name);
+
+    command
+        .arg("module")
+        .arg(module_name)
+        .env_clear()
+        .env("PATH", env!("PATH")) // Provide the $PATH variable so that external programs are runnable
+        .env("STARSHIP_CONFIG", EMPTY_CONFIG.as_os_str());
 
     command
 }
@@ -20,3 +41,21 @@ pub fn new_tempdir() -> io::Result<tempfile::TempDir> {
     // "/var/folders", which provides us with restricted permissions (rwxr-xr-x)
     tempfile::tempdir_in("/tmp")
 }
+
+/// Extends `std::process::Command` with methods for testing
+pub trait TestCommand {
+    fn use_config(&mut self, toml: toml::value::Value) -> &mut process::Command;
+}
+
+impl TestCommand for process::Command {
+    /// Create a configuration file with the provided TOML and use it
+    fn use_config(&mut self, toml: toml::value::Value) -> &mut process::Command {
+        // Create a persistent config file in a tempdir
+        let (mut config_file, config_path) =
+            tempfile::NamedTempFile::new().unwrap().keep().unwrap();
+        write!(config_file, "{}", toml.to_string()).unwrap();
+
+        // Set that newly-created file as the config for the prompt instance
+        self.env("STARSHIP_CONFIG", config_path)
+    }
+}