Add tests and docs for add_newline

docs/config/README.md

@@ -14,6 +14,9 @@ $ touch ~/.config/starship.toml
 All configuration for starship is done in this [TOML](https://github.com/toml-lang/toml) file:
 
 ```toml
+# Don't print a new line at the start of the prompt
+add_newline = false
+
 # Replace the "➜" symbol in the prompt with "❯"
 [character]      # The name of the module we are confguring is "character"
 symbol = "❯"     # The "symbol" segment is being set to "❯"
@@ -37,6 +40,24 @@ are segments within it. Every module also has a prefix and suffix that are the d
  "via "         "⬢"        "v10.4.1"       ""
 ```
 
+## Prompt
+
+This is the list of prompt-wide configuration options.
+
+### Options
+
+| Variable | Default | Description|
+| `add_newline` | `true` | Add a new line before the start of the prompt |
+
+### Example
+
+```toml
+# ~/.config/starship.toml
+
+# Disable the newline at the start of the prompt
+add_newline = false
+```
+
 ## Battery
 
 The `battery` module shows how charged the device's battery is and its current charging status.

src/print.rs

@@ -2,10 +2,10 @@ use clap::ArgMatches;
 use rayon::prelude::*;
 use std::io::{self, Write};
 
+use crate::config::Config;
 use crate::context::Context;
 use crate::module::Module;
 use crate::modules;
-use crate::config::Config;
 
 const PROMPT_ORDER: &[&str] = &[
     "battery",

tests/testsuite/common.rs

@@ -9,8 +9,8 @@ lazy_static! {
     static ref EMPTY_CONFIG: PathBuf = MANIFEST_DIR.join("empty_config.toml");
 }
 
-/// Run an instance of starship
-fn run_starship() -> process::Command {
+/// Render the full starship prompt
+pub fn render_prompt() -> process::Command {
     let mut command = process::Command::new("./target/debug/starship");
 
     command
@@ -22,6 +22,7 @@ fn run_starship() -> process::Command {
     command
 }
 
+/// Render a specific starship module by name
 pub fn render_module(module_name: &str) -> process::Command {
     let mut command = process::Command::new("./target/debug/starship");
 

tests/testsuite/configuration.rs

@@ -32,3 +32,24 @@ fn disabled_module() -> io::Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn add_newline_configuration() -> io::Result<()> {
+    // Start prompt with newline
+    let default_output = common::render_prompt().output()?;
+    let actual = String::from_utf8(default_output.stdout).unwrap();
+    let expected = actual.trim_start();
+    assert_ne!(actual, expected);
+
+    // Start prompt without newline
+    let output = common::render_prompt()
+        .use_config(toml::toml! {
+            add_newline = false
+        })
+        .output()?;
+    let actual = String::from_utf8(output.stdout).unwrap();
+    let expected = actual.trim_start();
+    assert_eq!(expected, actual);
+
+    Ok(())
+}