Test indentation level calculation (#6281)

Co-authored-by: Jonatan Pettersson <jonatan.pettersson@proton.me>

helix-core/tests/indent.rs

@@ -1,5 +1,5 @@
 use helix_core::{
-    indent::{treesitter_indent_for_pos, IndentStyle},
+    indent::{indent_level_for_line, treesitter_indent_for_pos, IndentStyle},
     syntax::Loader,
     Syntax,
 };
@@ -17,6 +17,39 @@ fn test_treesitter_indent_rust_2() {
     // test_treesitter_indent("commands.rs", "source.rust");
 }
 
+#[test]
+fn test_indent_level_for_line_with_spaces() {
+    let tab_width: usize = 4;
+    let indent_width: usize = 4;
+
+    let line = ropey::Rope::from_str("        Indented with 8 spaces");
+
+    let indent_level = indent_level_for_line(line.slice(0..), tab_width, indent_width);
+    assert_eq!(indent_level, 2)
+}
+
+#[test]
+fn test_indent_level_for_line_with_tabs() {
+    let tab_width: usize = 4;
+    let indent_width: usize = 4;
+
+    let line = ropey::Rope::from_str("\t\tIndented with 2 tabs");
+
+    let indent_level = indent_level_for_line(line.slice(0..), tab_width, indent_width);
+    assert_eq!(indent_level, 2)
+}
+
+#[test]
+fn test_indent_level_for_line_with_spaces_and_tabs() {
+    let tab_width: usize = 4;
+    let indent_width: usize = 4;
+
+    let line = ropey::Rope::from_str("   \t \tIndented with mix of spaces and tabs");
+
+    let indent_level = indent_level_for_line(line.slice(0..), tab_width, indent_width);
+    assert_eq!(indent_level, 2)
+}
+
 fn test_treesitter_indent(file_name: &str, lang_scope: &str) {
     let mut test_dir = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
     test_dir.push("tests/data/indent");