diff --git a/tests/php/Forms/EmailFieldTest.php b/tests/php/Forms/EmailFieldTest.php
index 9eeaa4915..85733d8a6 100644
--- a/tests/php/Forms/EmailFieldTest.php
+++ b/tests/php/Forms/EmailFieldTest.php
@@ -67,23 +67,16 @@ class EmailFieldTest extends FunctionalTest
      *
      * @see SimpleTagBuilder::_createInputTag()
      */
-    function testEmailFieldPopulation()
+    public function testEmailFieldPopulation()
     {
-
         $this->get('EmailFieldTest_Controller');
-        $this->submitForm(
+
+        $response = $this->submitForm(
             'Form_Form',
             null,
-            array(
-            'Email' => 'test@test.com'
-            )
+            ['Email' => 'test@test.com']
         );
 
-        $this->assertPartialMatchBySelector(
-            'p.good',
-            array(
-            'Test save was successful'
-            )
-        );
+        $this->assertContains('Test save was successful', $response->getBody());
     }
 }
diff --git a/tests/php/Forms/FormTest.php b/tests/php/Forms/FormTest.php
index ab7a91367..ae7e1d7bd 100644
--- a/tests/php/Forms/FormTest.php
+++ b/tests/php/Forms/FormTest.php
@@ -2,33 +2,31 @@
 
 namespace SilverStripe\Forms\Tests;
 
+use SilverStripe\Control\Controller;
+use SilverStripe\Control\HTTPRequest;
 use SilverStripe\Control\Session;
-use SilverStripe\Core\Config\Config;
+use SilverStripe\Dev\CSSContentParser;
+use SilverStripe\Dev\FunctionalTest;
+use SilverStripe\Forms\DateField;
+use SilverStripe\Forms\FieldList;
+use SilverStripe\Forms\FileField;
+use SilverStripe\Forms\Form;
+use SilverStripe\Forms\FormAction;
+use SilverStripe\Forms\HeaderField;
+use SilverStripe\Forms\LookupField;
+use SilverStripe\Forms\NumericField;
 use SilverStripe\Forms\PasswordField;
-use SilverStripe\Forms\Tests\FormTest\TestController;
 use SilverStripe\Forms\Tests\FormTest\ControllerWithSecurityToken;
 use SilverStripe\Forms\Tests\FormTest\ControllerWithStrictPostCheck;
 use SilverStripe\Forms\Tests\FormTest\Player;
 use SilverStripe\Forms\Tests\FormTest\Team;
+use SilverStripe\Forms\Tests\FormTest\TestController;
+use SilverStripe\Forms\TextareaField;
+use SilverStripe\Forms\TextField;
 use SilverStripe\ORM\ValidationResult;
 use SilverStripe\Security\NullSecurityToken;
-use SilverStripe\Security\Security;
-use SilverStripe\Security\SecurityToken;
 use SilverStripe\Security\RandomGenerator;
-use SilverStripe\Dev\CSSContentParser;
-use SilverStripe\Dev\FunctionalTest;
-use SilverStripe\Control\Controller;
-use SilverStripe\Control\HTTPRequest;
-use SilverStripe\Forms\TextField;
-use SilverStripe\Forms\FieldList;
-use SilverStripe\Forms\Form;
-use SilverStripe\Forms\HeaderField;
-use SilverStripe\Forms\TextareaField;
-use SilverStripe\Forms\DateField;
-use SilverStripe\Forms\NumericField;
-use SilverStripe\Forms\LookupField;
-use SilverStripe\Forms\FileField;
-use SilverStripe\Forms\FormAction;
+use SilverStripe\Security\SecurityToken;
 use SilverStripe\View\SSViewer;
 
 /**
@@ -50,6 +48,8 @@ class FormTest extends FunctionalTest
         ControllerWithStrictPostCheck::class,
     ];
 
+    protected static $disable_themes = true;
+
     protected function setUp()
     {
         parent::setUp();
diff --git a/tests/php/Forms/GridField/GridFieldDetailFormTest.php b/tests/php/Forms/GridField/GridFieldDetailFormTest.php
index 81d425867..9bc0226d8 100644
--- a/tests/php/Forms/GridField/GridFieldDetailFormTest.php
+++ b/tests/php/Forms/GridField/GridFieldDetailFormTest.php
@@ -2,20 +2,19 @@
 
 namespace SilverStripe\Forms\Tests\GridField;
 
-use SilverStripe\Dev\CSSContentParser;
-use SilverStripe\Dev\Debug;
-use SilverStripe\Dev\FunctionalTest;
 use SilverStripe\Control\Controller;
-use SilverStripe\Forms\HiddenField;
-use SilverStripe\Forms\GridField\GridFieldDetailForm;
+use SilverStripe\Dev\CSSContentParser;
+use SilverStripe\Dev\FunctionalTest;
 use SilverStripe\Forms\GridField\GridField;
+use SilverStripe\Forms\GridField\GridFieldDetailForm;
 use SilverStripe\Forms\GridField\GridFieldDetailForm_ItemRequest;
+use SilverStripe\Forms\HiddenField;
 use SilverStripe\Forms\Tests\GridField\GridFieldDetailFormTest\Category;
 use SilverStripe\Forms\Tests\GridField\GridFieldDetailFormTest\CategoryController;
-use SilverStripe\Forms\Tests\GridField\GridFieldDetailFormTest\TestController;
 use SilverStripe\Forms\Tests\GridField\GridFieldDetailFormTest\GroupController;
 use SilverStripe\Forms\Tests\GridField\GridFieldDetailFormTest\PeopleGroup;
 use SilverStripe\Forms\Tests\GridField\GridFieldDetailFormTest\Person;
+use SilverStripe\Forms\Tests\GridField\GridFieldDetailFormTest\TestController;
 
 /**
  * @skipUpgrade
@@ -36,6 +35,8 @@ class GridFieldDetailFormTest extends FunctionalTest
         GroupController::class,
     ];
 
+    protected static $disable_themes = true;
+
     public function testValidator()
     {
         $this->logInWithPermission('ADMIN');
diff --git a/tests/php/Forms/LookupFieldTest.php b/tests/php/Forms/LookupFieldTest.php
index c41b1b141..1f53a8234 100644
--- a/tests/php/Forms/LookupFieldTest.php
+++ b/tests/php/Forms/LookupFieldTest.php
@@ -5,90 +5,85 @@ namespace SilverStripe\Forms\Tests;
 use SilverStripe\ORM\DataObject;
 use SilverStripe\Dev\SapphireTest;
 use SilverStripe\Forms\LookupField;
+use SilverStripe\Security\Member;
 
 class LookupFieldTest extends SapphireTest
 {
-
     protected static $fixture_file = 'LookupFieldTest.yml';
 
     public function testNullValueWithNumericArraySource()
     {
         $source = array(1 => 'one', 2 => 'two', 3 => 'three');
-        $f = new LookupField('test', 'test', $source);
-        $f->setValue(null);
+        $field = new LookupField('test', 'test', $source);
+        $field->setValue(null);
+        $result = trim($field->Field()->getValue());
 
-        $this->assertEquals(
-            '<span class="readonly" id="test"><i>(none)</i></span><input type="hidden" name="test" value="" />',
-            trim($f->Field()->getValue())
-        );
+        $this->assertContains('<span class="readonly" id="test"><i>(none)</i></span>', $result);
+        $this->assertContains('<input type="hidden" name="test" value="" />', $result);
     }
 
     public function testStringValueWithNumericArraySource()
     {
         $source = array(1 => 'one', 2 => 'two', 3 => 'three');
-        $f = new LookupField('test', 'test', $source);
-        $f->setValue(1);
-        $this->assertEquals(
-            '<span class="readonly" id="test">one</span><input type="hidden" name="test" value="1" />',
-            trim($f->Field()->getValue())
-        );
+        $field = new LookupField('test', 'test', $source);
+        $field->setValue(1);
+        $result = trim($field->Field()->getValue());
+        $this->assertContains('<span class="readonly" id="test">one</span>', $result);
+        $this->assertContains('<input type="hidden" name="test" value="1" />', $result);
     }
 
     public function testUnknownStringValueWithNumericArraySource()
     {
         $source = array(1 => 'one', 2 => 'two', 3 => 'three');
-        $f = new LookupField('test', 'test', $source);
-        $f->setValue('w00t');
-        $this->assertEquals(
-            '<span class="readonly" id="test">w00t</span><input type="hidden" name="test" value="" />',
-            trim($f->Field()->getValue())
-        );
+        $field = new LookupField('test', 'test', $source);
+        $field->setValue('w00t');
+        $result = trim($field->Field()->getValue());
+
+        $this->assertContains('<span class="readonly" id="test">w00t</span>', $result);
+        $this->assertContains('<input type="hidden" name="test" value="" />', $result);
     }
 
     public function testArrayValueWithAssociativeArraySource()
     {
         // Array values (= multiple selections) might be set e.g. from ListboxField
         $source = array('one' => 'one val', 'two' => 'two val', 'three' => 'three val');
-        $f = new LookupField('test', 'test', $source);
-        $f->setValue(array('one','two'));
-        $this->assertEquals(
-            '<span class="readonly" id="test">one val, two val</span>'
-            . '<input type="hidden" name="test" value="one, two" />',
-            trim($f->Field()->getValue())
-        );
+        $field = new LookupField('test', 'test', $source);
+        $field->setValue(array('one','two'));
+        $result = trim($field->Field()->getValue());
+
+        $this->assertContains('<span class="readonly" id="test">one val, two val</span>', $result);
+        $this->assertContains('<input type="hidden" name="test" value="one, two" />', $result);
     }
 
     public function testArrayValueWithNumericArraySource()
     {
         // Array values (= multiple selections) might be set e.g. from ListboxField
         $source = array(1 => 'one', 2 => 'two', 3 => 'three');
-        $f = new LookupField('test', 'test', $source);
-        $f->setValue(array(1,2));
-        $this->assertEquals(
-            '<span class="readonly" id="test">one, two</span><input type="hidden" name="test" value="1, 2" />',
-            trim($f->Field()->getValue())
-        );
+        $field = new LookupField('test', 'test', $source);
+        $field->setValue(array(1,2));
+        $result = trim($field->Field()->getValue());
+
+        $this->assertContains('<span class="readonly" id="test">one, two</span>', $result);
+        $this->assertContains('<input type="hidden" name="test" value="1, 2" />', $result);
     }
 
     public function testArrayValueWithSqlMapSource()
     {
-        $member1 = $this->objFromFixture('SilverStripe\\Security\\Member', 'member1');
-        $member2 = $this->objFromFixture('SilverStripe\\Security\\Member', 'member2');
-        $member3 = $this->objFromFixture('SilverStripe\\Security\\Member', 'member3');
+        $member1 = $this->objFromFixture(Member::class, 'member1');
+        $member2 = $this->objFromFixture(Member::class, 'member2');
+        $member3 = $this->objFromFixture(Member::class, 'member3');
 
-        $source = DataObject::get('SilverStripe\\Security\\Member');
-        $f = new LookupField('test', 'test', $source->map('ID', 'FirstName'));
-        $f->setValue(array($member1->ID, $member2->ID));
+        $source = DataObject::get(Member::class);
+        $field = new LookupField('test', 'test', $source->map('ID', 'FirstName'));
+        $field->setValue(array($member1->ID, $member2->ID));
+        $result = trim($field->Field()->getValue());
 
-        $this->assertEquals(
-            sprintf(
-                '<span class="readonly" id="test">member1, member2</span>'
-                    . '<input type="hidden" name="test" value="%s, %s" />',
-                $member1->ID,
-                $member2->ID
-            ),
-            trim($f->Field()->getValue())
-        );
+        $this->assertContains('<span class="readonly" id="test">member1, member2</span>', $result);
+        $this->assertContains(sprintf(
+            '<input type="hidden" name="test" value="%s, %s" />',
+            $member1->ID,
+            $member2->ID
+        ), $result);
     }
 
     public function testWithMultiDimensionalSource()
@@ -105,23 +100,17 @@ class LookupFieldTest extends SapphireTest
             )
         );
 
-        $f = new LookupField('test', 'test', $choices);
-        $f->setValue(3);
+        $field = new LookupField('test', 'test', $choices);
+        $field->setValue(3);
+        $result = trim($field->Field()->getValue());
 
-        $this->assertEquals(
-            '<span class="readonly" id="test">Carrots</span><input type="hidden" name="test" value="3" />',
-            trim($f->Field()->getValue())
-        );
+        $this->assertContains('<span class="readonly" id="test">Carrots</span>', $result);
+        $this->assertContains('<input type="hidden" name="test" value="3" />', $result);
 
-        $f->setValue(
-            array(
-            3, 9
-            )
-        );
+        $field->setValue([3, 9]);
+        $result = trim($field->Field()->getValue());
 
-        $this->assertEquals(
-            '<span class="readonly" id="test">Carrots, Vegan</span><input type="hidden" name="test" value="3, 9" />',
-            trim($f->Field()->getValue())
-        );
+        $this->assertContains('<span class="readonly" id="test">Carrots, Vegan</span>', $result);
+        $this->assertContains('<input type="hidden" name="test" value="3, 9" />', $result);
     }
 }
diff --git a/tests/php/Forms/SelectionGroupTest.php b/tests/php/Forms/SelectionGroupTest.php
index 3c1d3e441..82ba88520 100644
--- a/tests/php/Forms/SelectionGroupTest.php
+++ b/tests/php/Forms/SelectionGroupTest.php
@@ -58,6 +58,7 @@ class SelectionGroupTest extends SapphireTest
         $field->setValue('two');
 
         $parser = new CSSContentParser($field->FieldHolder());
+
         $listEls = $parser->getBySelector('li');
         $listElOne = $listEls[0];
         $listElTwo = $listEls[1];
diff --git a/tests/php/Forms/TreeDropdownFieldTest.php b/tests/php/Forms/TreeDropdownFieldTest.php
index dfc49bbce..5b5e22fd1 100644
--- a/tests/php/Forms/TreeDropdownFieldTest.php
+++ b/tests/php/Forms/TreeDropdownFieldTest.php
@@ -196,15 +196,17 @@ class TreeDropdownFieldTest extends SapphireTest
     public function testReadonly()
     {
         $field = new TreeDropdownField('TestTree', 'Test tree', File::class);
-        $asdf = $this->objFromFixture(File::class, 'asdf');
-        $field->setValue($asdf->ID);
+        $fileMock = $this->objFromFixture(File::class, 'asdf');
+        $field->setValue($fileMock->ID);
         $readonlyField = $field->performReadonlyTransformation();
-        $this->assertEquals(
-            <<<"HTML"
-<span class="readonly" id="TestTree">&lt;Special &amp; characters&gt;</span><input type="hidden" name="TestTree" value="{$asdf->ID}" />
-HTML
-            ,
-            (string)$readonlyField->Field()
+        $result = (string) $readonlyField->Field();
+        $this->assertContains(
+            '<span class="readonly" id="TestTree">&lt;Special &amp; characters&gt;</span>',
+            $result
+        );
+        $this->assertContains(
+            '<input type="hidden" name="TestTree" value="' . $fileMock->ID . '" />',
+            $result
         );
     }
 }