How to test code dependent on environment variables using JUnit

Question

I have a piece of Java code which uses an environment variable and the behaviour of the code depends on the value of this variable  I would like to test this code with different values of the environment variable  How can I do this in JUnit   I ve seen some ways to set environment variables in Java in general  but I m more interested in unit testing aspect of it  especially considering that tests shouldn t interfere with each other

User · Answer

Well you can use the setup   method to declare the different values of your env  variables in constants   Then use these constants in the tests methods used to test the different scenario

User · Answer

You can use Powermock for mocking the call  Like  PowerMockito mockStatic System class   PowerMockito when System getenv  quot MyEnvVariable quot    thenReturn  quot DesiredValue quot     You can also mock all the calls with  PowerMockito mockStatic System class   PowerMockito when System getenv Mockito anyString     thenReturn envVariable

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In a similar situation like this where I had to write Test Case which is dependent on Environment Variable  I tried following    I went for System Rules as suggested by Stefan Birkner  Its use was simple  But sooner than later  I found the behavior erratic  In one run  it works  in the very next run it fails  I investigated and found that System Rules work well with JUnit 4 or higher version  But in my cases  I was using some Jars which were dependent on JUnit 3  So I skipped System Rules  More on it you can find here  Rule annotation doesn  39 t work while using TestSuite in JUnit  Next I tried to create Environment Variable through Process Builder class provided by Java  Here through Java Code we can create an environment variable  but you need to know the process or program name which I did not  Also it creates environment variable for child process  not for the main process    I wasted a day using the above two approaches  but of no avail  Then Maven came to my rescue  We can set Environment Variables or System Properties through Maven POM file which I think best way to do Unit Testing for Maven based project  Below is the entry I made in POM file        lt build gt         lt plugins gt          lt plugin gt           lt groupId gt org apache maven plugins lt  groupId gt           lt artifactId gt maven-surefire-plugin lt  artifactId gt           lt configuration gt             lt systemPropertyVariables gt                 lt PropertyName1 gt PropertyValue1 lt  PropertyName1 gt                                                                           lt PropertyName2 gt PropertyValue2 lt  PropertyName2 gt             lt  systemPropertyVariables gt             lt environmentVariables gt               lt EnvironmentVariable1 gt EnvironmentVariableValue1 lt  EnvironmentVariable1 gt               lt EnvironmentVariable2 gt EnvironmentVariableValue2 lt  EnvironmentVariable2 gt             lt  environmentVariables gt           lt  configuration gt         lt  plugin gt       lt  plugins gt     lt  build gt    After this change  I ran Test Cases again and suddenly all worked as expected  For reader s information  I explored this approach in Maven 3 x  so I have no idea on Maven 2 x

User · Answer

Decouple the Java code from the Environment variable providing a more abstract variable reader that you realize with an EnvironmentVariableReader your code to test reads from   Then in your test you can give an different implementation of the variable reader that provides your test values   Dependency injection can help in this

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Even though I think this answer is the best for Maven projects  It can be achieved via reflect as well  tested in Java 8    public class TestClass       private static final Map lt String  String gt  DEFAULTS   new HashMap lt  gt  System getenv         private static Map lt String  String gt  envMap        Test     public void aTest             assertEquals  6   System getenv  NUMBER OF PROCESSORS             System getenv   put  NUMBER OF PROCESSORS    155            assertEquals  155   System getenv  NUMBER OF PROCESSORS                 Test     public void anotherTest             assertEquals  6   System getenv  NUMBER OF PROCESSORS             System getenv   put  NUMBER OF PROCESSORS    77            assertEquals  77   System getenv  NUMBER OF PROCESSORS                          Restore default variables for each test              BeforeEach     public void initEnvMap             envMap clear            envMap putAll DEFAULTS               BeforeAll     public static void accessFields   throws Exception           envMap   new HashMap lt  gt             Class lt   gt  clazz   Class forName  java lang ProcessEnvironment            Field theCaseInsensitiveEnvironmentField   clazz getDeclaredField  theCaseInsensitiveEnvironment            Field theUnmodifiableEnvironmentField   clazz getDeclaredField  theUnmodifiableEnvironment            removeStaticFinalAndSetValue theCaseInsensitiveEnvironmentField  envMap           removeStaticFinalAndSetValue theUnmodifiableEnvironmentField  envMap              private static void removeStaticFinalAndSetValue Field field  Object value  throws Exception           field setAccessible true           Field modifiersField   Field class getDeclaredField  modifiers            modifiersField setAccessible true           modifiersField setInt field  field getModifiers    amp   Modifier FINAL           field set null  value

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The library https   github com webcompere system-stubs tree master system-stubs-jupiter - a fork of system-lambda - provides a JUnit 5 plug-in   ExtendWith SystemStubsExtension class  class SomeTest        SystemStub     private EnvironmentVariables environmentVariables          new EnvironmentVariables  quot name quot    quot value quot          Test     void someTest               environment is set here            can set a new value into the environment too        environmentVariables set  quot other quot    quot value quot               tidy up happens at end of this test           The https   junit-pioneer org  alternative requires environment variable values to be known at compile time  The above also supports the setting of environment variables in the  BeforeAll  which means it interoperates well with things like Testcontainers that might set up some resources needed by child tests

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I don t think this has been mentioned yet  but you could also use Powermockito   Given   package com foo service impl   public class FooServiceImpl        public void doSomeFooStuff             System getenv  FOO VAR 1            System getenv  FOO VAR 2            System getenv  FOO VAR 3                Do the other Foo stuff           You could do the following   package com foo service impl   import static org mockito Mockito when  import static org powermock api mockito PowerMockito mockStatic  import static org powermock api mockito PowerMockito verifyStatic   import org junit Beforea  import org junit Test  import org junit runner RunWith  import org mockito InjectMocks  import org mockito MockitoAnnotations  import org powermock core classloader annotations PrepareForTest  import org powermock modules junit4 PowerMockRunner    RunWith PowerMockRunner class   PrepareForTest FooServiceImpl class  public class FooServiceImpTest         InjectMocks     private FooServiceImpl service        Before     public void setUp             MockitoAnnotations initMocks this            mockStatic System class       Powermock can mock static and private methods          when System getenv  FOO VAR 1    thenReturn  test-foo-var-1            when System getenv  FOO VAR 2    thenReturn  test-foo-var-2            when System getenv  FOO VAR 3    thenReturn  test-foo-var-3                Test     public void testSomeFooStuff                        Test         service doSomeFooStuff             verifyStatic            System getenv  FOO VAR 1            verifyStatic            System getenv  FOO VAR 2            verifyStatic            System getenv  FOO VAR 3

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If you want to retrieve informations about the environment variable in Java  you can call the method   System getenv     As the properties  this method returns a Map containing  the variable names as keys and the variable values as the map values  Here is an example         import java util Map   public class EnvMap       public static void main  String   args            Map lt String  String gt  env   System getenv            for  String envName   env keySet                  System out format   s  s n   envName  env get envName                        The method getEnv   can also takes an argument  For instance    String myvalue   System getEnv  MY VARIABLE      For testing  I would do something like this     public class Environment       public static String getVariable String variable           return  System getenv variable       Test  public class EnvVariableTest          Test testVariable1             String value   Environment getVariable  MY VARIABLE1             doSometest value                 Test testVariable2           String value2   Environment getVariable  MY VARIABLE2           doSometest value

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The library System Lambda has a method withEnvironmentVariables for setting environment variables  public void EnvironmentVariablesTest      Test   public void setEnvironmentVariable         String value   withEnvironmentVariable  quot name quot    quot value quot          execute    - gt  System getenv  quot name quot         assertEquals  quot value quot   value          For Java 5 to 7 the library System Rules has a JUnit rule called EnvironmentVariables  import org junit contrib java lang system EnvironmentVariables   public class EnvironmentVariablesTest      Rule   public final EnvironmentVariables environmentVariables       new EnvironmentVariables        Test   public void setEnvironmentVariable         environmentVariables set  quot name quot    quot value quot        assertEquals  quot value quot   System getenv  quot name quot            Full disclosure  I m the author of both libraries

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One slow  dependable  old-school method that always works in every operating system with every language  and even between languages  is to write the  quot system environment quot  data you need to a temporary text file  read it when you need it  and then erase it   Of course  if you re running in parallel  then you need unique names for the file  and if you re putting sensitive information in it  then you need to encrypt it

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The usual solution is to create a class which manages the access to this environmental variable  which you can then mock in your test class   public class Environment       public String getVariable             return System getenv       or whatever          public class ServiceTest       private static class MockEnvironment           public String getVariable                return  foobar                         Test public void testService             service doSomething new MockEnvironment               The class under test then gets the environment variable using the Environment class  not directly from System getenv

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I use System getEnv   to get the map and I keep as a field  so I can mock it   public class AAA        Map lt String  String gt  environmentVars        public String readEnvironmentVar String varName            if  environmentVars  null  environmentVars   System getenv               return environmentVars get varName              public class AAATest              Test          public void test                   aaa environmentVars   new HashMap lt String String gt                   aaa environmentVars put  NAME    value                  assertEquals  value  aaa readEnvironmentVar  NAME

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I think the cleanest way to do this is with Mockito spy    It s a bit more lightweight than creating a separate class to mock and pass around   Move your environment variable fetching to another method    VisibleForTesting String getEnvironmentVariable String envVar        return System getenv envVar       Now in your unit test do this    Test public void test         ClassToTest classToTest   new ClassToTest        ClassToTest classToTestSpy   Mockito spy classToTest       Mockito when classToTestSpy getEnvironmentVariable  key    thenReturn  value           Now test the method that uses getEnvironmentVariable     assertEquals  changedvalue   classToTestSpy methodToTest

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For JUnit 4 users  System Lambda as suggested by Stefan Birkner is a great fit  In case you are using JUnit 5  there is the JUnit Pioneer extension pack  It comes with  ClearEnvironmentVariable and  SetEnvironmentVariable  From the docs   The  ClearEnvironmentVariable and  SetEnvironmentVariable annotations can be used to clear  respectively  set the values of environment variables for a test execution  Both annotations work on the test method and class level  are repeatable as well as combinable  After the annotated method has been executed  the variables mentioned in the annotation will be restored to their original value or will be cleared if they didn t have one before  Other environment variables that are changed during the test  are not restored   Example   Test  ClearEnvironmentVariable key    quot SOME VARIABLE quot    SetEnvironmentVariable key    quot ANOTHER VARIABLE quot   value    quot new value quot   void test         assertNull System getenv  quot SOME VARIABLE quot         assertEquals  quot new value quot   System getenv  quot ANOTHER VARIABLE quot

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A lot of focus in the suggestions above on inventing ways in runtime to pass in variables  set them and clear them and so on    But to test things  structurally   I guess you want to have different test suites for different scenarios  Pretty much like when you want to run your  heavier  integration test builds  whereas in most cases you just want to skip them  But then you don t try and  invent ways to set stuff in runtime   rather you just tell maven what you want  It used to be a lot of work telling maven to run specific tests via profiles and such  if you google around people would suggest doing it via springboot  but if you haven t dragged in the springboot monstrum into your project  it seems a horrendous footprint for  just running JUnits   right    Or else it would imply loads of more or less inconvenient POM XML juggling which is also tiresome and  let s just say it   a nineties move   as inconvenient as still insisting on making  spring beans out of XML   showing off your ultimate 600 line logback xml or whatnot     Nowadays  you can just use Junit 5  this example is for maven  more details can be found here JUnit 5 User Guide 5    lt dependencyManagement gt       lt dependencies gt           lt dependency gt               lt groupId gt org junit lt  groupId gt               lt artifactId gt junit-bom lt  artifactId gt               lt version gt 5 7 0 lt  version gt               lt type gt pom lt  type gt               lt scope gt import lt  scope gt           lt  dependency gt       lt  dependencies gt   lt  dependencyManagement gt   and then      lt dependency gt           lt groupId gt org junit jupiter lt  groupId gt           lt artifactId gt junit-jupiter lt  artifactId gt           lt scope gt test lt  scope gt       lt  dependency gt   and then in your favourite utility lib create a simple nifty annotation class such as  Target   ElementType TYPE  ElementType METHOD     Retention RetentionPolicy RUNTIME   EnabledIfEnvironmentVariable named    quot MAVEN CMD LINE ARGS quot   matches    quot     integration-testing     quot   public  interface IntegrationTest     so then whenever your cmdline options contain -Pintegration-testing for instance  then and only then will your  IntegrationTest annotated test-class method fire  Or  if you don t want to use  and setup  a specific maven profile but rather just pass in  trigger  system properties by means of mvn  lt cmds gt  -DmySystemPop mySystemPropValue  and adjust your annotation interface to trigger on that  yes  there is also a  EnabledIfSystemProperty   Or making sure your shell is set up to contain  whatever you need  or  as is suggested above  actually going through  the pain  adding system env via your POM XML  Having your code internally in runtime fiddle with env or mocking env  setting it up and then possibly  clearing  runtime env to change itself during execution just seems like a bad  perhaps even dangerous  approach - it s easy to imagine someone will always sooner or later make a  hidden  internal mistake that will go unnoticed for a while  just to arise suddenly and bite you hard in production later    You usually prefer an approach entailing that  given input  gives  expected output   something that is easy to grasp and maintain over time  your fellow coders will just see it  immediately   Well long  answer  or maybe rather just an opinion on why you d prefer this approach  yes  at first I just read the heading for this question and went ahead to answer that  ie  How to test code dependent on environment variables using JUnit

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Hope the issue is resolved  I just thought to tell my solution   Map lt String  String gt  env   System getenv        new MockUp lt System gt               Mock                    public String getenv String name                         if  name equalsIgnoreCase   OUR OWN VARIABLE                       return  true                             return env get name

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This answer to the question How do I set environment variables from Java  provides a way to alter the  unmodifiable  Map in System getenv    So while it doesn t REALLY change the value of the OS environment variable  it can be used for unit testing as it does change what System getenv will return

[java] How to test code dependent on environment variables using JUnit?

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