I figured it out! I had to point the classpath to the compiled jar file for the Android library project, which lives in the bin folder, and then provide JUnit with the fully qualified name of the class. My final script looks as follows:
#!/bin/sh
echo Starting test...
cd ./Android/iSENSE\ Imports/
java -cp ./bin/isense\ imports.jar:./lib/junit-4.10.jar \
org.junit.runner.JUnitCore edu.uml.cs.isense.test.APITest
echo Test complete!