Theme Builder: structured color/type controls, scheme catalog, diverging preview

src/core/custom-theme.test.ts

@@ -88,4 +88,20 @@ describe('THEME_PREVIEW_SPECS', () => {
     const ids = THEME_PREVIEW_SPECS.map((c) => c.id);
     expect(new Set(ids).size).toBe(ids.length);
   });
+
+  it('exercises every color family the builder controls', () => {
+    type ColorDef = { type?: string; scale?: { domainMid?: unknown } };
+    const colorOf = (spec: (typeof THEME_PREVIEW_SPECS)[number]['spec']): ColorDef | undefined =>
+      (spec.encoding as { color?: ColorDef } | undefined)?.color;
+
+    const colors = THEME_PREVIEW_SPECS.map((c) => colorOf(c.spec));
+    // mark.color (a card with no color encoding), categorical, sequential
+    // (quantitative, no midpoint), and diverging (quantitative with a midpoint).
+    expect(colors.some((c) => c === undefined)).toBe(true);
+    expect(colors.some((c) => c?.type === 'nominal')).toBe(true);
+    expect(colors.some((c) => c?.type === 'quantitative' && c.scale?.domainMid === undefined)).toBe(
+      true,
+    );
+    expect(colors.some((c) => c?.scale?.domainMid !== undefined)).toBe(true);
+  });
 });