Adding tests for AttributedSpans.contractAttributions

Author: jmatth

attributed_text/test/attributed_spans_test.dart

@@ -632,6 +632,83 @@ void main() {
         expect(span1 == span2, isFalse);
       });
     });
+
+    group('contract attributions', () {
+      group('empty attributions', () {
+        test('start at 0, length 0', () {
+          final spans = AttributedSpans();
+          final contractedSpans = spans.copy()..contractAttributions(startOffset: 0, count: 0);
+          expect(contractedSpans, spans);
+        });
+
+        test('start at 0, length 10', () {
+          final spans = AttributedSpans();
+          final contractedSpans = spans.copy()..contractAttributions(startOffset: 0, count: 10);
+          expect(contractedSpans, spans);
+        });
+
+        test('start at 0, length 10', () {
+          final spans = AttributedSpans();
+          final contractedSpans = spans.copy()..contractAttributions(startOffset: 5, count: 10);
+        });
+      });
+
+      group('single attribution', () {
+        test('contract after of attribution', () {
+          final spans = AttributedSpans()..addAttribution(newAttribution: ExpectedSpans.bold, start: 0, end: 5);
+          final contractedSpans = spans.copy()..contractAttributions(startOffset: 6, count: 5);
+          expect(contractedSpans, spans);
+        });
+
+        test('contract before attribution', () {
+          final spans = AttributedSpans()..addAttribution(newAttribution: ExpectedSpans.bold, start: 5, end: 10);
+          final contractedSpans = spans.copy()..contractAttributions(startOffset: 0, count: 5);
+          expect(
+            contractedSpans,
+            AttributedSpans()
+              ..addAttribution(
+                newAttribution: ExpectedSpans.bold,
+                start: 0,
+                end: 5,
+              ),
+          );
+        });
+
+        test('contract around attribution', () {
+          final spans = AttributedSpans()..addAttribution(newAttribution: ExpectedSpans.bold, start: 5, end: 10);
+          final contractedSpans = spans.copy()..contractAttributions(startOffset: 5, count: 6);
+          expect(contractedSpans.markers, isEmpty);
+        });
+
+        test('contract from start to middle of attribution', () {
+          final spans = AttributedSpans()..addAttribution(newAttribution: ExpectedSpans.bold, start: 5, end: 10);
+          final contractedSpans = spans.copy()..contractAttributions(startOffset: 5, count: 3);
+          expect(
+            contractedSpans,
+            AttributedSpans()
+              ..addAttribution(
+                newAttribution: ExpectedSpans.bold,
+                start: 5,
+                end: 7,
+              ),
+          );
+        });
+
+        test('contract from middle to end of attribution', () {
+          final spans = AttributedSpans()..addAttribution(newAttribution: ExpectedSpans.bold, start: 5, end: 10);
+          final contractedSpans = spans.copy()..contractAttributions(startOffset: 7, count: 3);
+          expect(
+            contractedSpans,
+            AttributedSpans()
+              ..addAttribution(
+                newAttribution: ExpectedSpans.bold,
+                start: 5,
+                end: 7,
+              ),
+          );
+        });
+      });
+    });
   });
 }