Posted onOct 31, 2020

Replace method with JavaParser library

Motivation

Recently I want to migrate from JUnitassertEquals to HamcrestassertThat andis to improve readability of my unit tests.

Instead of using regular expression, it seems it is safer to parse the syntax and manipulate it, so I chooseJavaParser.

Objective

Here is how existing test looks like.

packagecom.franzwong.playground;importorg.junit.jupiter.api.Test;importstaticorg.junit.jupiter.api.Assertions.assertEquals;classMyTest{@Testpublicvoidtest(){Stringa="123";assertEquals("123",a);}}

I would like to change it to something like this.

packagecom.franzwong.playground;importorg.junit.jupiter.api.Test;importstaticorg.hamcrest.MatcherAssert.assertThat;importstaticorg.hamcrest.CoreMatchers.is;classMyTest{@Testpublicvoidtest(){Stringa="123";assertThat(a,is("123"));}}

Action items:

Remove the static import ofassertEquals
Add static import forassertThat andis
ConvertassertEquals("123", a) toassertThat(a, is("123"))
Save modified source

Solution

Add Maven dependency for JavaParser

<dependency><groupId>com.github.javaparser</groupId><artifactId>javaparser-core</artifactId><version>3.16.2</version></dependency>

Setup`CompilationUnit`

SupposeMyTest.java file is stored in/tmp folder.

SourceRootsourceRoot=newSourceRoot(Path.of("/tmp"));CompilationUnitcu=sourceRoot.parse("","MyTest.java");

Remove the static import of`assertEquals`

We just need to walk through the syntax tree. If the import declaration node is found and it is theassertEquals node, we just remove it.

cu.walk(ImportDeclaration.class,e->{if(e.isStatic()&&"org.junit.jupiter.api.Assertions.assertEquals".equals(e.getNameAsString())){e.remove();}});

Add static import for`assertThat` and`is`

Parameters of ImportDeclaration constructor

1st parameter is the static method name
2nd parameter is true if it is a static import
3rd parameter is true if it is asterisk

cu.addImport(newImportDeclaration("org.hamcrest.MatcherAssert.assertThat",true,false));cu.addImport(newImportDeclaration("org.hamcrest.CoreMatchers.is",true,false));

Convert`assertEquals("123", a)` to`assertThat(a, is("123"))`

We walk through the syntax tree again. If it is aMethodCallExpr node and its name isassertEquals, we rename it and change its parameters.

cu.walk(MethodCallExpr.class,e->{if(!"assertEquals".equals(e.getNameAsString())){return;}// Rename methode.setName("assertThat");// Get the parameter list of `assertEquals`NodeList<Expression>equalsArgments=e.getArguments();// Create a new `is` method and assign 1st parameter of `assertEquals` to itMethodCallExprisMethod=newMethodCallExpr("is",equalsArgments.get(0));// Change the parametersequalsArgments.set(0,equalsArgments.get(1));equalsArgments.set(1,isMethod);});

Save modified source

We just need to provide a folder path to it.

sourceRoot.saveAll(Path.of("/tmp/output"));

So that's it. Here is how the whole source code looks like. I hope this tutorial is useful to you.

publicstaticvoidmain(String[]args){SourceRootsourceRoot=newSourceRoot(Path.of("/tmp"));CompilationUnitcu=sourceRoot.parse("","MyTest.java");cu.walk(ImportDeclaration.class,e->{if(e.isStatic()&&"org.junit.jupiter.api.Assertions.assertEquals".equals(e.getNameAsString())){e.remove();}});cu.addImport(newImportDeclaration("org.hamcrest.MatcherAssert.assertThat",true,false));cu.addImport(newImportDeclaration("org.hamcrest.CoreMatchers.is",true,false));cu.walk(MethodCallExpr.class,e->{if(!"assertEquals".equals(e.getNameAsString())){return;}// Rename methode.setName("assertThat");// Get the parameter list of `assertEquals`NodeList<Expression>equalsArgments=e.getArguments();// Create a new `is` method and assign 1st parameter of `assertEquals` to itMethodCallExprisMethod=newMethodCallExpr("is",equalsArgments.get(0));// Change the parametersequalsArgments.set(0,equalsArgments.get(1));equalsArgments.set(1,isMethod);});sourceRoot.saveAll(Path.of("/tmp/output"));}