fix: Change panicking on unknown module to error print and support module listing flag (#197)

tests/testsuite/main.rs

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

tests/testsuite/modules.rs

@@ -0,0 +1,31 @@
+use std::io;
+
+use crate::common;
+
+#[test]
+fn unknown_module_name() -> io::Result<()> {
+    let unknown_module_name = "some_random_name";
+    let output = common::render_module(unknown_module_name).output()?;
+    let actual_stdout = String::from_utf8(output.stdout).unwrap();
+    let actual_stderr = String::from_utf8(output.stderr).unwrap();
+    let expected_stdout = "";
+    let expected_stderr = format!(
+        "Error: Unknown module {}. Use starship module --list to list out all supported modules.\n",
+        unknown_module_name
+    );
+    assert_eq!(expected_stdout, actual_stdout);
+    assert_eq!(expected_stderr, actual_stderr);
+    Ok(())
+}
+
+#[test]
+fn known_module_name() -> io::Result<()> {
+    let output = common::render_module("line_break").output()?;
+    let actual_stdout = String::from_utf8(output.stdout).unwrap();
+    let actual_stderr = String::from_utf8(output.stderr).unwrap();
+    let expected_stdout = "\n";
+    let expected_stderr = "";
+    assert_eq!(expected_stdout, actual_stdout);
+    assert_eq!(expected_stderr, actual_stderr);
+    Ok(())
+}