1 files changed, 113 insertions, 0 deletions
diff --git a/spec/frontend/helpers/diffs_helper_spec.js b/spec/frontend/helpers/diffs_helper_spec.js
new file mode 100644
index 00000000000..b223d48bf5c
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+++ b/spec/frontend/helpers/diffs_helper_spec.js
@@ -0,0 +1,113 @@
+import * as diffsHelper from '~/helpers/diffs_helper';
+
+describe('diffs helper', () => {
+  function getDiffFile(withOverrides = {}) {
+    return {
+      parallel_diff_lines: ['line'],
+      highlighted_diff_lines: ['line'],
+      blob: {
+        readable_text: 'text',
+      },
+      ...withOverrides,
+    };
+  }
+
+  describe('hasInlineLines', () => {
+    it('is false when the file does not exist', () => {
+      expect(diffsHelper.hasInlineLines()).toBeFalsy();
+    });
+
+    it('is false when the file does not have the highlighted_diff_lines property', () => {
+      const missingInline = getDiffFile({ highlighted_diff_lines: undefined });
+
+      expect(diffsHelper.hasInlineLines(missingInline)).toBeFalsy();
+    });
+
+    it('is false when the file has zero highlighted_diff_lines', () => {
+      const emptyInline = getDiffFile({ highlighted_diff_lines: [] });
+
+      expect(diffsHelper.hasInlineLines(emptyInline)).toBeFalsy();
+    });
+
+    it('is true when the file has at least 1 highlighted_diff_lines', () => {
+      expect(diffsHelper.hasInlineLines(getDiffFile())).toBeTruthy();
+    });
+  });
+
+  describe('hasParallelLines', () => {
+    it('is false when the file does not exist', () => {
+      expect(diffsHelper.hasParallelLines()).toBeFalsy();
+    });
+
+    it('is false when the file does not have the parallel_diff_lines property', () => {
+      const missingInline = getDiffFile({ parallel_diff_lines: undefined });
+
+      expect(diffsHelper.hasParallelLines(missingInline)).toBeFalsy();
+    });
+
+    it('is false when the file has zero parallel_diff_lines', () => {
+      const emptyInline = getDiffFile({ parallel_diff_lines: [] });
+
+      expect(diffsHelper.hasParallelLines(emptyInline)).toBeFalsy();
+    });
+
+    it('is true when the file has at least 1 parallel_diff_lines', () => {
+      expect(diffsHelper.hasParallelLines(getDiffFile())).toBeTruthy();
+    });
+  });
+
+  describe('isSingleViewStyle', () => {
+    it('is true when the file has at least 1 inline line but no parallel lines for any reason', () => {
+      const noParallelLines = getDiffFile({ parallel_diff_lines: undefined });
+      const emptyParallelLines = getDiffFile({ parallel_diff_lines: [] });
+
+      expect(diffsHelper.isSingleViewStyle(noParallelLines)).toBeTruthy();
+      expect(diffsHelper.isSingleViewStyle(emptyParallelLines)).toBeTruthy();
+    });
+
+    it('is true when the file has at least 1 parallel line but no inline lines for any reason', () => {
+      const noInlineLines = getDiffFile({ highlighted_diff_lines: undefined });
+      const emptyInlineLines = getDiffFile({ highlighted_diff_lines: [] });
+
+      expect(diffsHelper.isSingleViewStyle(noInlineLines)).toBeTruthy();
+      expect(diffsHelper.isSingleViewStyle(emptyInlineLines)).toBeTruthy();
+    });
+
+    it('is true when the file does not have any inline lines or parallel lines for any reason', () => {
+      const noLines = getDiffFile({
+        highlighted_diff_lines: undefined,
+        parallel_diff_lines: undefined,
+      });
+      const emptyLines = getDiffFile({
+        highlighted_diff_lines: [],
+        parallel_diff_lines: [],
+      });
+
+      expect(diffsHelper.isSingleViewStyle(noLines)).toBeTruthy();
+      expect(diffsHelper.isSingleViewStyle(emptyLines)).toBeTruthy();
+      expect(diffsHelper.isSingleViewStyle()).toBeTruthy();
+    });
+
+    it('is false when the file has both inline and parallel lines', () => {
+      expect(diffsHelper.isSingleViewStyle(getDiffFile())).toBeFalsy();
+    });
+  });
+
+  describe.each`
+    context                                     | inline       | parallel     | blob                         | expected
+    ${'only has inline lines'}                  | ${['line']}  | ${undefined} | ${undefined}                 | ${true}
+    ${'only has parallel lines'}                | ${undefined} | ${['line']}  | ${undefined}                 | ${true}
+    ${"doesn't have inline, parallel, or blob"} | ${undefined} | ${undefined} | ${undefined}                 | ${true}
+    ${'has blob readable text'}                 | ${undefined} | ${undefined} | ${{ readable_text: 'text' }} | ${false}
+  `('when hasDiff', ({ context, inline, parallel, blob, expected }) => {
+    it(`${context}`, () => {
+      const diffFile = getDiffFile({
+        highlighted_diff_lines: inline,
+        parallel_diff_lines: parallel,
+        blob,
+      });
+
+      expect(diffsHelper.hasDiff(diffFile)).toEqual(expected);
+    });
+  });
+});