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Testing Bidirectional Text Processing Functionality in PDF.js

This test suite evaluates the bidirectional text handling functionality in Mozilla’s PDF.js library. It verifies the correct processing and display of mixed left-to-right (LTR) and right-to-left (RTL) text content, ensuring proper text direction detection and rendering across different scenarios.

Test Coverage Overview

The test suite provides comprehensive coverage of bidirectional text processing scenarios.

Key areas tested include:

LTR text detection for short strings
LTR text detection for longer content
RTL text detection above 30% threshold
RTL text detection below 30% threshold
Edge case handling for very short strings with RTL characters

Implementation Analysis

The testing approach uses Jasmine framework’s describe/it pattern to structure test cases. Each test validates the bidi() function’s output, checking both the processed string and its determined direction (str and dir properties). The implementation specifically focuses on the 30% threshold rule for RTL text detection and handles special cases for very short strings.

Technical patterns include:

Unicode character testing
Threshold-based direction detection
String length edge cases

Technical Details

Testing tools and configuration:

Jasmine test framework
Module import system for bidi functionality
Unicode character testing support
Custom expect assertions for string and direction validation
Parameterized test cases for different scenarios

Best Practices Demonstrated

The test suite exemplifies strong testing practices through clear test case organization and comprehensive scenario coverage.

Notable practices include:

Descriptive test case naming
Isolated test scenarios
Clear input/output validation
Edge case consideration
Regression test coverage (issue 11656)

mozilla/pdfJs

test/unit/bidi_spec.js

            
/* Copyright 2017 Mozilla Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import { bidi } from "../../src/core/bidi.js";

describe("bidi", function () {
  it(
    "should mark text as LTR if there's only LTR-characters, " +
      "when the string is very short",
    function () {
      const str = "foo";
      const bidiText = bidi(str, -1, false);

      expect(bidiText.str).toEqual("foo");
      expect(bidiText.dir).toEqual("ltr");
    }
  );

  it("should mark text as LTR if there's only LTR-characters", function () {
    const str = "Lorem ipsum dolor sit amet, consectetur adipisicing elit.";
    const bidiText = bidi(str, -1, false);

    expect(bidiText.str).toEqual(
      "Lorem ipsum dolor sit amet, consectetur adipisicing elit."
    );
    expect(bidiText.dir).toEqual("ltr");
  });

  it("should mark text as RTL if more than 30% of text is RTL", function () {
    // 33% of test text are RTL characters
    const test = "\u0645\u0635\u0631 Egypt";
    const result = "Egypt \u0631\u0635\u0645";
    const bidiText = bidi(test, -1, false);

    expect(bidiText.str).toEqual(result);
    expect(bidiText.dir).toEqual("rtl");
  });

  it("should mark text as LTR if less than 30% of text is RTL", function () {
    const test = "Egypt is known as \u0645\u0635\u0631 in Arabic.";
    const result = "Egypt is known as \u0631\u0635\u0645 in Arabic.";
    const bidiText = bidi(test, -1, false);

    expect(bidiText.str).toEqual(result);
    expect(bidiText.dir).toEqual("ltr");
  });

  it(
    "should mark text as RTL if less than 30% of text is RTL, " +
      "when the string is very short (issue 11656)",
    function () {
      const str = "()\u05d1("; // 25% of the string is RTL characters.
      const bidiText = bidi(str, -1, false);

      expect(bidiText.str).toEqual("(\u05d1)(");
      expect(bidiText.dir).toEqual("rtl");
    }
  );
});