Writing tests for the AspectJ compiler

The AspectJ project has a harness which reads test specification files and run tests. The tests are usually simple scenarios like "compile and run" or "compile expecting error", but may involve multiple files, incremental compilation, classpath or aspectpath entries, etc. This document shows how to write tests that can be run by the harness and suggests some patterns to use in test code, discussing

Simple test definitions
Test source files
Incremental tests
Verifying test steps

Messages
Changes in an output directory
Runtime behavior

Compiler Options
Harness background

Most people just writing a test case need to know only the information in Simple test definitions and Test source files.

Simple Test definitions

Here is a simple example to compile Main.java and expect an error on line 10:

    <ajc-test dir="new" title="simple error test">
        <compile files="Main.java">
            <message kind="error" line="10"/>
        </compile>
    </ajc-test>

Here is an example to compile pack/Aspect.java and pack2/Main.java and run the main class:

    <ajc-test dir="new" title="simple run test">
        <compile files="pack/Aspect.java,pack1/Main.java"/>
        <run class="pack1.Main"/>
    </ajc-test>

The compile and run steps of a given ajc-test share a common sandbox, so (e.g.,) the run step knows to set its classpath using the classes directory generated by the compile step.

More complex compilations are discussed in Compiler Options below.

Test source files

The dir attribute in the ajc-test element specifies a base test directory relative to the directory of the test specification file. All paths are specified relative to this base test directory. E.g., the last example used dir="new" and presumed the following directory structure:

    {some dir}                  # test specification directory
        {testDefinition}.xml
        new/                    # test base directory
          pack/Aspect.java
          pack2/Main.java

Test cases with only one file in the default package can often share directories (e.g., see the many files in new/), but usually a test case has its own directory.

Incremental tests

Incremental tests are more complex because they involve updating source files before recompiling. Here's an example that

compiles Main.java,
runs it,
updates the source to introduce an error,
incrementally compile it (and detect the error)
updates the source to fix the error,
incrementally compile it (successfully), and
runs it again.

    <ajc-test dir="new/incremental1" title="incremental test">
        <compile staging="true"
                   files="Main.java,DeleteMe.java"/>
        <run class="Main"/>
        <inc-compile tag="20">
            <message kind="error" line="15">
        </inc-compile>
        <inc-compile tag="30"/>
        <run class="Main"/>
    </ajc-test>

Take particular note of two attributes, compile's "staging" and inc-compile's "tag". First, the compile task enables staging, which copies the test source files to a temporary directory so they can be updated during the test without changing the actual sources. Second, incremental compiles specify a tag which identifies files to be deleted or copied into the test source staging directory before recompiling. The tag is a suffix identifying files in the test source directory specifying how the sources should be changed before that incremental compilation step. If there is a prefixing suffix "delete", then the file is deleted; otherwise, the file is copied (with the effect either of updating an existing file or adding a new file).

Thus, to understand what's happening in an incremental test requires comparing the tags with the files specified in the test source directory. For example, here is a directory layout for the test above:

    {some dir}
        {testDefinition}.xml
        new/
          incremental1/
            DeleteMe.delete.30.java
            DeleteMe.java
            Main.20.java
            Main.30.java
            Main.java
            NewFile.30.java

The result will be one compile and two re-compiles:

Initially compile Main.java and DeleteMe.java

    <compile staging="true"
              files="Main.java,DeleteMe.java"/>

    {some dir}
        {testDefinition}.xml
        new/
          incremental1/
            ...
            DeleteMe.java
            ...
            Main.java
            ...

For incremental tag 20, update Main.java with the contents of Main.20.java and recompile, expecting an error on line 15:

    <inc-compile tag="20">
        <message kind="error" line="15">
    </inc-compile>

    {some dir}
        {testDefinition}.xml
        new/
          incremental1/
            ...
            Main.20.java
            ...

For incremental tag 30, delete DeleteMe.java, add NewFile.java, update Main.java with the contents of Main.30.java and recompile with no error or warning messages:

    <inc-compile tag="30"/>

    {some dir}
        {testDefinition}.xml
        new/
          incremental1/
            DeleteMe.delete.30.java
            ...
            Main.30.java
            ...
            NewFile.30.java

Verifying test steps

As seen above, two ways to verify that a compile was successful are to run the corresponding class or check the compiler messages. More generally, the harness can verify compile/run test steps by detecting the following things and comparing against expected behavior:

Detect Evaluate

Exceptions signal failure

Result value heuristically compare with expected: compiles not expecting errors are expected to return a normal result status, and vice-versa.

Messages (e.g., compiler warnings and errors) Compare with expected messages

Directory changes (e.g., .class files created) Compare with expected changes

Runtime behavior Use Tester in test source code to signal events for comparison with expected events.

Detect	Evaluate
Exceptions	signal failure
Result value	heuristically compare with expected: compiles not expecting errors are expected to return a normal result status, and vice-versa.
Messages (e.g., compiler warnings and errors)	Compare with expected messages
Directory changes (e.g., `.class` files created)	Compare with expected changes
Runtime behavior	Use `Tester` in test source code to signal events for comparison with expected events.

Messages

In a test definition, a nested message element specifies a condition on the successful completion of the nesting ajc-test sub-element. In the earlier example, if the harness does not detect an error message on line 10 or if there are unexpected messages, then the compile step will be reported as failing:

    <ajc-test dir="new" title="simple error test">
        <compile files="Main.java">
            <message kind="error" line="10"/>
        </compile>
    </ajc-test>

Expected messages can be specified as sub-elements for the three ajc-test elements compile, inc-compile, and run. Messages require a kind (error or warning) and a line. To make specification easier, if an error is specified for a line, the harness accepts as expected any number of errors on that line.

The current harness has only been tested to validate compilation based on line numbers. Filename-based comparison is disabled as untested/unused, and run messages are handled wrongly; line-number comparison will fail since run messages do not have line numbers.

Changes in an output directory

As with messages, specifying directory changes as a nested element operates as a condition on the successful completion of the nesting element. The harness will check for files added, removed, updated, or unchanged from a given directory. The directory is specified explicitly or using a token for the shared classes or run directory. For even more brevity, the harness supports a default suffix for the files.

Directory changes have been used only to validate changes in the classes directory. The current harness defaults to using the classes directory, and when using the classes directory uses .class as a default suffix.

Here's an example specification:

    <ajc-test dir="new/dirchanges-test" title="dir-changes test">
        <compile staging="true"
                   files="Main.java,DeleteMe.java,Unchanged.java"/>
        <inc-compile tag="20">
            <dir-changes updated="Main" 
                         removed="DeleteMe"
                       unchanged="Unchanged"/>
        </inc-compile>
    </ajc-test>

It checks after a recompile that

Main.class was updated
DeleteMe.class was deleted
Unchanged.class was not touched

Runtime behavior

Code that tests aspects often falls into the pattern of comparing expected and actual events/signals. For example, to prove that before advice in fact ran before a particular method execution, you might generated and expect signals corresponding to

method-call
before advice execution
method-execution

The Tester utility class provides API's for signalling actual and expecting events and comparing the two. Typically, events are symbolized and compared as String. Here's a small sample test case that for the scenario above:

import org.aspectj.testing.Tester;

public class Main implements Runnable {
    public static void main(String[] args) {
        Tester.expectEvent("before advice");
        Tester.expectEvent("execute run");
        new Main().run();     
        Tester.checkAllEvents();
    }
    public void run() {
        Tester.event("execute run");
    }
}

aspect A {
    before () : target(Runnable) && execution(void run()) {
         Tester.event("before advice");
    }
}

If either the advice or the method does not run, the harness will report a failure.

Tester also has methods that operate like JUnit assertions as idioms to detect differences in expected and actual values, signalling appropriately.

Tester is at ../testing-client/src/org/aspectj/testing/Tester.java and is built into ../lib/tests/testing-client.jar which is included on the classpath by the compile and run steps.

You can write runtime test cases without using Tester; simply throw some exception from the main thread to signal failure.

Compiler options

The harness does not support all of the AspectJ 1.1 compiler options. Flags are mainly supported through the a comma-delimited list in the options attribute:

    <ajc-test dir="new" title="lint test">
        <compile files="LintTest.java" 
                 options="-Xlint,-emacssym">
            <message kind="warning" line="22">
        </compile>

This should work even for complex single-arg options like -g:none, but will fail for comma-delimited single-arg options like -g:lines,vars because the comma delimiters are ambiguous (yes, a design bug!). For -source 1.4 and -source 1.3 options, use -source14 and -source13 (yes, a hack!).

The compile element has the following attributes which handle most of the other compiler arguments:

files: .aj and .java files are treated as source files, but .jar files are extracted and passed to the compiler as -injars
classpath: directories and jar files for the classpath
aspectpath: binary aspects in jar files
argfiles: argument list files

Paths for these are all relative to the test base directory, and multiple entries are separated with commas.

Here is a cooked example that uses all compiler attributes:

    <ajc-test dir="new" title="attributes test">
        <compile files="Main.java,injar.jar" 
               staging="true"
               options="-Xlint,-g:none"
              argfiles="debug.lst,aspects/test.lst"
            aspectpath="jars/requiredAspects.jar"
             classpath="providedClassesDir,jars/required.jar"/>
        <inc-compile tag="20"/>
    </ajc-test>

Unsupported compiler options

The harness does not support the following AspectJ compiler options: -target {version}, -outjar {file}, -sourceroots {dir}, -log {file}. The following are used but specification is not supported: -d {dir}, -sourceroots {dir}...

Background information on the Harness

To make the test specifications as terse as possible, harness components for inc-compile and run elements use information set up earlier by compile, some of which is only implicit. When a test is run, the harness creates a staging directory for temporary files and a sandbox component for sharing information between test components, particularly classpath entries shared between the compile and run components. The compile and run components share classpath information through the sandbox, adding default libraries:

Aside from any explicit classpath entries, compile always includes the jars ../lib/tests/aspecjrt.jar and ../lib/tests/testing-client.jar on the compile classpath.
run sets up its classpath as the compile classpath plus the compile output (classes) directory plus any entries on the aspectpath.

The harness provides some more advance behaviors, which you might see specified in the tests. For more information, see the API documentation for the harness.

option dominance and overriding: Both in test specifications and on the command line you can force compiler options on or off. (Forcing means that, e.g., even if an option is enabled in the test specification, it can be disabled from the command line.) These appear in the test specifications as options with prefixes '!' or '~' rather than '-' (e.g., '~emacssym' to force the emacssym option off, even in tests that specify it).

last updated January 29, 2002