test: Add missing test file for UI sparkline component

Implemented test coverage for the `buildSparkline` UI function using a lightweight manual mock of `document.createElementNS`. Verified SVG attributes, logic when points are uniform, and logic for dynamically rendering polyline coordinates and conclusion dots based on data points.

src/ui/sparkline.test.ts

@@ -0,0 +1,115 @@
+import { describe, it, expect, beforeEach, afterEach, vi } from "vitest";
+import { buildSparkline } from "./sparkline";
+
+describe("buildSparkline", () => {
+  beforeEach(() => {
+    vi.stubGlobal("document", {
+      createElementNS: vi.fn((ns, tag) => {
+        const attributes: Record<string, string> = {};
+        const classes: string[] = [];
+        const children: any[] = [];
+        const style: Record<string, string> = {};
+
+        return {
+          tagName: tag,
+          namespaceURI: ns,
+          setAttribute: vi.fn((key, val) => {
+            attributes[key] = val;
+          }),
+          getAttribute: vi.fn((key) => attributes[key]),
+          classList: {
+            add: vi.fn((cls) => {
+              classes.push(cls);
+            }),
+            contains: vi.fn((cls) => classes.includes(cls)),
+          },
+          style,
+          appendChild: vi.fn((child) => {
+            children.push(child);
+          }),
+          _getAttributes: () => attributes,
+          _getClasses: () => classes,
+          _getChildren: () => children,
+        };
+      }),
+    });
+  });
+
+  afterEach(() => {
+    vi.unstubAllGlobals();
+  });
+
+  it("creates a base SVG element with correct attributes and style", () => {
+    const pts = [10, 20, 30];
+    const svg = buildSparkline(pts, 150) as any;
+
+    expect(document.createElementNS).toHaveBeenCalledWith("http://www.w3.org/2000/svg", "svg");
+    expect(svg.tagName).toBe("svg");
+    expect(svg._getAttributes()).toMatchObject({
+      width: "80",
+      height: "20",
+      viewBox: "0 0 80 20",
+    });
+    expect(svg._getClasses()).toContain("result-sparkline");
+    expect(svg.style.top).toBe("150px");
+  });
+
+  it("appends a straight line when all points are equal (min === max)", () => {
+    const pts = [10, 10, 10];
+    const svg = buildSparkline(pts, 0) as any;
+
+    const children = svg._getChildren();
+    expect(children.length).toBe(1);
+
+    const line = children[0];
+    expect(line.tagName).toBe("line");
+    expect(line._getAttributes()).toMatchObject({
+      x1: "2",
+      y1: "10",
+      x2: "78",
+      y2: "10",
+      stroke: "var(--result)",
+      "stroke-width": "1.5",
+    });
+  });
+
+  it("appends a polyline and a circle for varying points", () => {
+    const pts = [10, 20, 30]; // min=10, max=30
+    const svg = buildSparkline(pts, 0) as any;
+
+    const children = svg._getChildren();
+    expect(children.length).toBe(2);
+
+    const polyline = children[0];
+    expect(polyline.tagName).toBe("polyline");
+    expect(polyline._getAttributes()).toMatchObject({
+      fill: "none",
+      stroke: "var(--result)",
+      "stroke-width": "1.5",
+      "stroke-linecap": "round",
+      "stroke-linejoin": "round",
+    });
+
+    // Check points calculation
+    const pointsStr = polyline._getAttributes().points;
+    expect(typeof pointsStr).toBe("string");
+    const points = pointsStr.split(" ");
+    expect(points.length).toBe(3);
+
+    // First point should be at x=2 (pad), y=18 (H-pad because value is min)
+    expect(points[0]).toBe("2.0,18.0");
+    // Middle point should be at x=40 (pad + W/2), y=10 (pad + H/2 because value is mid)
+    expect(points[1]).toBe("40.0,10.0");
+    // Last point should be at x=78 (W-pad), y=2 (pad because value is max)
+    expect(points[2]).toBe("78.0,2.0");
+
+    const circle = children[1];
+    expect(circle.tagName).toBe("circle");
+    expect(circle._getAttributes()).toMatchObject({
+      cx: "78.0",
+      cy: "2.0",
+      r: "2",
+      fill: "var(--result)",
+    });
+  });
+});