Hi,

I have a trigger which prevents duplicate contacts being entered into Salesforce. When creating the test class, I'm getting this error:
"Initial term of field expression must be a concrete SObject: LIST<Contact>" on this line:
  

Below is the test class:

@isTest
public class TestContactDupeCatcher {
    static testMethod void testContactDupeCatcher() {    
      // First make sure there are no contacts already in the system
      // that have the email addresses used for testing
      Set<String> testEmailAddress = new Set<String>();
      testEmailAddress.add('test1@duptest.com');
      testEmailAddress.add('test2@duptest.com');
      testEmailAddress.add('test3@duptest.com');
      testEmailAddress.add('test4@duptest.com');
      testEmailAddress.add('test5@duptest.com');
      System.assert([SELECT count() FROM Contact
                     WHERE Email IN :testEmailAddress] == 0);
      // Seed the database with some contact, and make sure they can
      // be bulk inserted successfully.
      Contact contact1 = new Contact(LastName='Test1',
                            Email='test1@duptest.com');
      Contact contact2 = new Contact(LastName='Test2',
                            Email='test4@duptest.com');
      Contact contact3 = new Contact(LastName='Test3',
                            Email='test5@duptest.com');
      Contact[] contact = new Contact[] {contact1, contact2, contact3};
      insert contact;     
      // Now make sure that some of these contacts can be changed and
      // then bulk updated successfully. Note that contact1 is not
      // being changed, but is still being passed to the update
      // call. This should be OK.
      contact2.Email = 'test2@duptest.com';
      contact3.Email = 'test3@duptest.com';
      update contact;
      // Make sure that single row contact duplication prevention works
      // on insert.
      Contact dup1 = new Contact(LastName='Test1Dup',
                           Email='test1@duptest.com');
      try {
         insert dup1;
         System.assert(false);
      } catch (DmlException e) {
         System.assert(e.getNumDml() == 1);
         System.assert(e.getDmlIndex(0) == 0);
         System.assert(e.getDmlFields(0).size() == 1);
         System.assert(e.getDmlFields(0)[0].getDescribe().getName() == 'Email');
         System.assert(e.getDmlMessage(0).indexOf(
            'A contact with this email address already exists.') > -1);
      }
      // Make sure that single row lead duplication prevention works
      // on update.
      dup1 = new Contact(Id = contact1.Id, LastName='Test1Dup',
                      Email='test2@duptest.com');
      try {
         update dup1;
         System.assert(false);
      } catch (DmlException e) {
         System.assert(e.getNumDml() == 1);
         System.assert(e.getDmlIndex(0) == 0);
         System.assert(e.getDmlFields(0).size() == 1);
         System.assert(e.getDmlFields(0)[0].getDescribe().getName() == 'Email');
         System.assert(e.getDmlMessage(0).indexOf(
            'A contact with this email address already exists.') > -1);
        }
      // Make sure that bulk contact duplication prevention works on
      // insert. Note that the first item being inserted is fine,
      // but the second and third items are duplicates. Note also
      // that since at least one record insert fails, the entire
      // transaction will be rolled back.
      dup1 = new Contact(LastName='Test1Dup',
                      Email='test4@duptest.com');
      Contact dup2 = new Contact(LastName='Test2Dup',
                           Email='test2@duptest.com');
      Contact dup3 = new Contact(LastName='Test3Dup',
                           Email='test3@duptest.com');
      Contact[] dups = new Contact[] {dup1, dup2, dup3};
      try {
         insert dups;
         System.assert(false);
      } catch (DmlException e) {
         System.assert(e.getNumDml() == 2);
         System.assert(e.getDmlIndex(0) == 1);
         System.assert(e.getDmlFields(0).size() == 1);
         System.assert(e.getDmlFields(0)[0].getDescribe().getName() == 'Email');
         System.assert(e.getDmlMessage(0).indexOf(
            'A contact with this email address already exists.') > -1);
         System.assert(e.getDmlIndex(1) == 2);
         System.assert(e.getDmlFields(1).size() == 1);
         System.assert(e.getDmlFields(1)[0].getDescribe().getName() == 'Email');
         System.assert(e.getDmlMessage(1).indexOf(
            'A contact with this email address already exists.') > -1);
      }
      // Make sure that bulk contact duplication prevention works on
      // update. Note that the first item being updated is fine,
      // because the email address is new, and the second item is
      // also fine, but in this case it's because the email
      // address doesn't change. The third case is flagged as an
      // error because it is a duplicate of the email address of the
      // first contact's value in the database, even though that value
      // is changing in this same update call. It would be an
      // interesting exercise to rewrite the trigger to allow this
      // case. Note also that since at least one record update
      // fails, the entire transaction will be rolled back.
      dup1 = new Contact(Id=contact1.Id, Email='test4@duptest.com');
      dup2 = new Contact(Id=contact2.Id, Email='test2@duptest.com');
      dup3 = new Contact(Id=contact.Id, Email='test1@duptest.com');
      dups = new Contact[] {dup1, dup2, dup3};
      try {
         update dups;
         System.assert(false);
      } catch (DmlException e) {
         System.debug(e.getNumDml());
         System.debug(e.getDmlMessage(0));
         System.assert(e.getNumDml() == 1);
         System.assert(e.getDmlIndex(0) == 2);
         System.assert(e.getDmlFields(0).size() == 1);
         System.assert(e.getDmlFields(0)[0].getDescribe().getName() == 'Email');
         System.assert(e.getDmlMessage(0).indexOf(
            'A contact with this email address already exists.') > -1);
        }
      // Make sure that duplicates in the submission are caught when
      // inserting contacts. Note that this test also catches an
      // attempt to insert a contact where there is an existing
      // duplicate.
      dup1 = new Contact(LastName='Test1Dup',
                      Email='test4@duptest.com');
      dup2 = new Contact(LastName='Test2Dup',
                      Email='test4@duptest.com');
      dup3 = new Contact(LastName='Test3Dup',
                      Email='test3@duptest.com');
      dups = new Contact[] {dup1, dup2, dup3};
      try {
         insert dups;
         System.assert(false);
      } catch (DmlException e) {
         System.assert(e.getNumDml() == 2);
         System.assert(e.getDmlIndex(0) == 1);
         System.assert(e.getDmlFields(0).size() == 1);
         System.assert(e.getDmlFields(0)[0].getDescribe().getName() == 'Email');
         System.assert(e.getDmlMessage(0).indexOf(
            'Another new contact has the same email address.') > -1);
         System.assert(e.getDmlIndex(1) == 2);
         System.assert(e.getDmlFields(1).size() == 1);
         System.assert(e.getDmlFields(1)[0].getDescribe().getName() == 'Email');
         System.assert(e.getDmlMessage(1).indexOf(
            'A contact with this email address already exists.') > -1);
      }      
      // Make sure that duplicates in the submission are caught when
      // updating contacts. Note that this test also catches an attempt
      // to update a contact where there is an existing duplicate.
      dup1 = new Contact(Id=contact1.Id, Email='test4@duptest.com');
      dup2 = new Contact(Id=contact2.Id, Email='test4@duptest.com');
      dup3 = new Contact(Id=contact3.Id, Email='test2@duptest.com');
      dups = new Contact[] {dup1, dup2, dup3};
      try {
         update dups;
         System.assert(false);
      } catch (DmlException e) {
         System.assert(e.getNumDml() == 2);
         System.assert(e.getDmlIndex(0) == 1);
         System.assert(e.getDmlFields(0).size() == 1);
         System.assert(e.getDmlFields(0)[0].getDescribe().getName() == 'Email');
         System.assert(e.getDmlMessage(0).indexOf(
            'Another new contact has the same email address.') > -1);
         System.assert(e.getDmlIndex(1) == 2);
         System.assert(e.getDmlFields(1).size() == 1);
         System.assert(e.getDmlFields(1)[0].getDescribe().getName() == 'Email');
         System.assert(e.getDmlMessage(1).indexOf(
            'A contact with this email address already exists.') > -1);
      }
   }
}

Can someone help me with this error? Thanks!