.ai import: tests for Pattern brushes' number counts and an older Art brush's first number

A Pattern brush reads its scale from 3 or more numbers (the older form's
8 too) and isn't read with fewer; an 8-number Art brush is the older form
whatever its first number. The module notes say the count tells the form.

crates/eps/src/import/ai/brush.rs

@@ -28,10 +28,11 @@
 //!   [`vectorcraft_brush::ArtBrush`]'s `overlap: false`).
 //! - A Scatter, Art or Pattern brush's parameters are fields split by `/`: a number, the art's
 //!   section names (one for Scatter, five for Art and Pattern, empty where there is none, each
-//!   after a space for Art and Pattern), more fields, and last 15 numbers. Brushes whose first
-//!   number is 1, as older files write them, have one field fewer before the numbers and 8 numbers;
-//!   an Art brush in that form is read from its art's name alone (its numbers aren't known, so it
-//!   keeps the defaults and its paths their drawn look).
+//!   after a space for Art and Pattern), more fields, and last 15 numbers. Older files write
+//!   brushes with first number 1, one field fewer before the numbers and 8 numbers; an Art brush
+//!   with 8 numbers, whatever its first number, is read from its art's name alone (its numbers
+//!   aren't known, so it keeps the defaults and its paths their drawn look). A Pattern brush needs
+//!   only its first 3 numbers (its scale is the third).
 //!   - Scatter: the size (2, 3), spacing (5, 6) and scatter (8, 9) as (low, high) factors of the
 //!     art, the rotation in degrees (11, 12), how each varies (4, 7, 10, 13) and whether the
 //!     rotation follows the path (14), and 1 Tints (1).
@@ -339,7 +340,8 @@ pub(super) fn parse_tool_object(kind: Tool, name: &str, params: &str) -> Result<
                 }
                 Tool::Art => {
                     // The older form's 8 numbers aren't known: its brush keeps the defaults and its
-                    // paths their drawn look. Any other count isn't a form this reads.
+                    // paths their drawn look. The count tells the form, not the first number.
+                    // Any other count isn't a form this reads.
                     let (colorization, plain) = if let Ok(n15) = <&[f64; 15]>::try_from(n.as_slice()) {
                         (if n15[1] == 1.0 { Colorization::Tints } else { Colorization::None }, art_is_plain(n15))
                     } else if n.len() == 8 {

crates/eps/src/import/ai/tests.rs

@@ -8225,6 +8225,10 @@ fn an_older_art_brush_comes_in_with_its_art() {
         assert_eq!(brush::parse_tool_object(brush::Tool::Art, "Ribbon", bad), Err(brush::BrushError::Values), "{bad}");
     }
     assert_eq!(brush::parse_tool_object(brush::Tool::Scatter, "Spray", "1 /Dot art/ 0 1 /  1 0 1 0 1 0 0 0"), Err(brush::BrushError::Values));
+    // 8 numbers are the older form whatever the first number says: read with the defaults.
+    let d = brush::parse_tool_object(brush::Tool::Art, "Ribbon", "0 / Ribbon art/ / / / / 0 1 /  1 0 1 0 1 0 0 0").unwrap();
+    let brush::DraftKind::Art { ref brush, ref art, plain } = d.kind else { panic!("art") };
+    assert_eq!((art.as_str(), plain, brush.colorization), ("Ribbon art", false, vectorcraft_brush::ArtBrush::default().colorization));
     let objects = [plugin_object(ART_BRUSH, "Ribbon", OLD_RIBBON), plugin_object(ART_BRUSH, "Bare", "1 / / / / / / 0 1 /  1 0 1 0 1 0 0 0")].concat();
     let r = read_ok(&format!("{}{objects}{}", brush_art("Ribbon art", 4.0), layer("")));
     let lib = vectorcraft_brush::library(&r.doc);
@@ -8234,6 +8238,26 @@ fn an_older_art_brush_comes_in_with_its_art() {
     assert!(r.warnings.iter().any(|w| w.ends_with("Brushes panel (1)")), "{:?}", r.warnings);
 }
 
+/// A Pattern brush needs only its first 3 numbers, its scale the third (as a percentage), so the
+/// older form's 8 numbers read too; fewer than 3 aren't read.
+#[test]
+fn a_pattern_brush_reads_its_scale_from_three_or_more_numbers() {
+    const SLOTS: &str = "1 / Tile one/ Tile two/ / / Tile five/ 0 1 / ";
+    for numbers in ["1 0 0.5", "1 0 0.5 0 1 0 0 0"] {
+        let d = brush::parse_tool_object(brush::Tool::Pattern, "Fence", &format!("{SLOTS}{numbers}")).unwrap();
+        let brush::DraftKind::Pattern { tiles, scale } = d.kind else { panic!("{d:?}") };
+        assert_eq!(tiles[1].as_deref(), Some("Tile two"), "{numbers}");
+        assert!((scale - 50.0).abs() < 1e-9, "{numbers}: {scale}");
+    }
+    for numbers in ["", "1", "1 0"] {
+        assert_eq!(
+            brush::parse_tool_object(brush::Tool::Pattern, "Fence", &format!("{SLOTS}{numbers}")),
+            Err(brush::BrushError::Values),
+            "{numbers:?}"
+        );
+    }
+}
+
 /// A brush's art filled with a pattern the file defines before it is read, with that pattern.
 #[test]
 fn a_brushs_art_takes_the_patterns_defined_before_it() {