1 files changed, 80 insertions, 0 deletions
diff --git a/spec/frontend/ide/lib/diff/diff_spec.js b/spec/frontend/ide/lib/diff/diff_spec.js
new file mode 100644
index 00000000000..57f3ac3d365
--- /dev/null
+++ b/spec/frontend/ide/lib/diff/diff_spec.js
@@ -0,0 +1,80 @@
+import { computeDiff } from '~/ide/lib/diff/diff';
+
+describe('Multi-file editor library diff calculator', () => {
+  describe('computeDiff', () => {
+    it('returns empty array if no changes', () => {
+      const diff = computeDiff('123', '123');
+
+      expect(diff).toEqual([]);
+    });
+
+    describe('modified', () => {
+      it('', () => {
+        const diff = computeDiff('123', '1234')[0];
+
+        expect(diff.added).toBeTruthy();
+        expect(diff.modified).toBeTruthy();
+        expect(diff.removed).toBeUndefined();
+      });
+
+      it('', () => {
+        const diff = computeDiff('123\n123\n123', '123\n1234\n123')[0];
+
+        expect(diff.added).toBeTruthy();
+        expect(diff.modified).toBeTruthy();
+        expect(diff.removed).toBeUndefined();
+        expect(diff.lineNumber).toBe(2);
+      });
+    });
+
+    describe('added', () => {
+      it('', () => {
+        const diff = computeDiff('123', '123\n123')[0];
+
+        expect(diff.added).toBeTruthy();
+        expect(diff.modified).toBeUndefined();
+        expect(diff.removed).toBeUndefined();
+      });
+
+      it('', () => {
+        const diff = computeDiff('123\n123\n123', '123\n123\n1234\n123')[0];
+
+        expect(diff.added).toBeTruthy();
+        expect(diff.modified).toBeUndefined();
+        expect(diff.removed).toBeUndefined();
+        expect(diff.lineNumber).toBe(3);
+      });
+    });
+
+    describe('removed', () => {
+      it('', () => {
+        const diff = computeDiff('123', '')[0];
+
+        expect(diff.added).toBeUndefined();
+        expect(diff.modified).toBeUndefined();
+        expect(diff.removed).toBeTruthy();
+      });
+
+      it('', () => {
+        const diff = computeDiff('123\n123\n123', '123\n123')[0];
+
+        expect(diff.added).toBeUndefined();
+        expect(diff.modified).toBeTruthy();
+        expect(diff.removed).toBeTruthy();
+        expect(diff.lineNumber).toBe(2);
+      });
+    });
+
+    it('includes line number of change', () => {
+      const diff = computeDiff('123', '')[0];
+
+      expect(diff.lineNumber).toBe(1);
+    });
+
+    it('includes end line number of change', () => {
+      const diff = computeDiff('123', '')[0];
+
+      expect(diff.endLineNumber).toBe(1);
+    });
+  });
+});