Revert "Added function usage to support functional interface."

This reverts commit aa56581.

Author: martin-helmich

tests/Functional/JsonValueMatchesFluentTest.php

@@ -2,10 +2,6 @@
 namespace Helmich\JsonAssert\Tests\Functional;
 
 use PHPUnit\Framework\TestCase;
-use function PHPUnit\Framework\assertThat;
-use function PHPUnit\Framework\equalTo;
-use function PHPUnit\Framework\greaterThanOrEqual;
-use function PHPUnit\Framework\logicalNot;
 
 class JsonValueMatchesFluentTest extends TestCase
 {
@@ -32,18 +28,18 @@ class JsonValueMatchesFluentTest extends TestCase
 
     public function testAssertThatJsonDocumentContainsJsonValue()
     {
-        assertThat(self::$exampleDocument, containsJsonValue('$.identifier', 1234));
+        $this->assertThat(self::$exampleDocument, containsJsonValue('$.identifier', 1234));
     }
 
     public function testAssertThatJsonDocumentMatchesJsonConstraints()
     {
-        assertThat(
+        $this->assertThat(
             self::$exampleDocument,
             matchesJsonConstraints(
                 [
-                    '$.owner.name' => equalTo('Max Mustermann'),
-                    '$.products[*].identifier' => greaterThanOrEqual(500),
-                    '$.products[*].name' => logicalNot(equalTo('Weißbrot'))
+                    '$.owner.name' => $this->equalTo('Max Mustermann'),
+                    '$.products[*].identifier' => $this->greaterThanOrEqual(500),
+                    '$.products[*].name' => $this->logicalNot($this->equalTo('Weißbrot'))
                 ]
             )
         );

tests/Functional/JsonValueMatchesSchemaFluentTest.php

@@ -4,7 +4,6 @@
 use Helmich\JsonAssert\JsonAssertions;
 use PHPUnit\Framework\AssertionFailedError;
 use PHPUnit\Framework\TestCase;
-use function PHPUnit\Framework\assertThat;
 
 class JsonValueMatchesSchemaFluentTest extends TestCase
 {
@@ -32,7 +31,7 @@ class JsonValueMatchesSchemaFluentTest extends TestCase
 
     public function testJsonDocumentMatchesSchema()
     {
-        assertThat(static::$exampleDocument, matchesJsonSchema([
+        $this->assertThat(static::$exampleDocument, matchesJsonSchema([
             'type'       => 'object',
             'required'   => ['identifier', 'owner', 'products'],
             'properties' => [
@@ -65,7 +64,7 @@ public function testJsonDocumentDoesNotMatchSchema()
     {
         $this->expectException(AssertionFailedError::class);
 
-        assertThat(static::$exampleDocument, matchesJsonSchema([
+        $this->assertThat(static::$exampleDocument, matchesJsonSchema([
             'type' => 'object',
             'required' => ['foobar'],
             'properties' => [