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Validating Float Resource Type Safety in ButterKnife

This integration test suite validates the type checking functionality of ButterKnife’s @BindFloat annotation. It specifically tests error handling when attempting to bind float resources to incompatible field types, ensuring robust type safety in the Android view binding process.

Test Coverage Overview

The test coverage focuses on the failure handling of ButterKnife’s float resource binding mechanism. It verifies:

Type validation for @BindFloat annotation
Error message accuracy when binding to incorrect types
Exception handling for invalid field type assignments

Implementation Analysis

The testing approach employs JUnit to validate type safety constraints in ButterKnife’s view binding system. It utilizes a mock view tree structure and implements negative testing patterns to verify proper exception handling when attempting to bind float resources to String fields.

Technical Details

Testing tools and configuration include:

JUnit test framework
Google Truth assertion library
ButterKnife annotation processor
Mock View hierarchy
Custom ViewTree test utility

Best Practices Demonstrated

The test demonstrates several quality testing practices:

Explicit exception message validation
Clear test method naming
Proper test isolation
Comprehensive error case coverage
Clean test setup with minimal boilerplate

jakewharton/butterknife

butterknife-integration-test/src/androidTestReflect/java/com/example/butterknife/functional/BindFloatFailureTest.java

            
package com.example.butterknife.functional;

import android.view.View;
import butterknife.BindFloat;
import butterknife.ButterKnife;
import org.junit.Test;

import static com.google.common.truth.Truth.assertThat;
import static org.junit.Assert.fail;

public final class BindFloatFailureTest {
  private final View tree = ViewTree.create(1);

  static class Target {
    @BindFloat(1) String actual;
  }

  @Test public void typeMustBeFloat() {
    Target target = new Target();

    try {
      ButterKnife.bind(target, tree);
      fail();
    } catch (IllegalStateException e) {
      assertThat(e).hasMessageThat()
          .isEqualTo("@BindFloat field type must be 'float'. "
              + "(com.example.butterknife.functional.BindFloatFailureTest$Target.actual)");
    }
  }
}