Fixed flaky test case in EmailTest.java

[hermya]

Fixed flaky test case in the following class: org.simplejavamail.api.email.EmailTest

Assertion called in: EmailTest#testToStringFull

POINT OF FAILURE

In EmailPopulatingBuilderImpl class, headers was of type HashMap. HashMap being unordered, can give non-deterministic results for toString() method when run on different jvms.
Observed failure was:

expectedEmailString ~ "...headers={dummyHeader1=[dummyHeaderValue1], dummyHeader2=[dummyHeaderValue2]}..."
actualEmailString ~ "...headers={dummyHeader2=[dummyHeaderValue2], dummyHeader1=[dummyHeaderValue1]}..."

FIX

Changed the type of headers to LinkedHashMap as it retrieves the order of insertion in the Map, guaranteeing consistent toString() output.

Fixed using NonDex

Suggested command to check flaky tests :

mvn edu.illinois:nondex-maven-plugin:2.1.7:nondex

For the particular test class:

mvn -pl ./modules/simple-java-mail edu.illinois:nondex-maven-plugin:2.1.7:nondex \
-Dmode=ONE \
-DnondexRuns=5  \
-Dtest=org.simplejavamail.api.email.EmailTest#testToStringFull \
-Dossindex.skip=true -Dspotbugs.skip=true \
-Dmaven.javadoc.skip=true -Denforcer.skip=true \
-Djacoco.skip=true -Dlicense.skip=true

For more information: https://github.com/TestingResearchIllinois/NonDex