Convert a string timezone offset to a formatted string timezone offset

MyTimeTest.php

<?php
use PHPUnit\Framework\TestCase;

class MyTime {
    /**
     * Convert a float string timezone offset to a DateTimeZone
     *
     * @param string $number  The initial offset float, as a string.
     * @return DateTimeZone  The converted DateTimeZone
     */
    public function get_timezone_from_string( $time_string ) {
        $offset = $this->get_time_offset_from_number( $time_string );
        return new DateTimeZone( 'Etc/GMT' . $offset );
    }

    /**
     * Convert a string timezone offset to a formatted string timezone offset
     *
     * Converts the form '-6.5' to '-6:30'
     *
     * @param string $number  The initial offset.
     * @return string  The formatted offset
     */
    public function get_time_offset_from_number( $number ) {
        $offset = $number * 1; // type conversion: string to int/float
        if ( ! $offset ) {
            return null;
        }
        if ( is_int( $offset ) ) {
            return $number;
        }
        $hours = $offset < 0 ? '-' . abs( (int) $offset ) : '+' . (int) $offset;
        $minutes = abs( fmod( $offset, 1 ) ) * 60;
        return $hours . ':' . $minutes;
    }
}

class MyTimeTest extends TestCase {
    public function testGetZoneWithNegative() {
        $time = new MyTime();
        $zone = $time->get_timezone_from_string( '-6' );
        $this->assertEquals( new DateTimeZone( 'Etc/GMT-6' ), $zone );
    }

    public function testGetOffsetWithNegative() {
        $time = new MyTime();
        $offset = $time->get_time_offset_from_number( '-6' );
        $this->assertEquals( '-6', $offset );
    }

    public function testGetZoneWithPositive() {
        $time = new MyTime();
        $zone = $time->get_timezone_from_string( '+6' );
        $this->assertEquals( new DateTimeZone( 'Etc/GMT+6' ), $zone );
    }

    public function testGetOffsetWithPositive() {
        $time = new MyTime();
        $offset = $time->get_time_offset_from_number( '+6' );
        $this->assertEquals( '+6', $offset );
    }

    public function testGetOffsetWithFraction() {
        $time = new MyTime();
        $offset = $time->get_time_offset_from_number( '+6.5' );
        $this->assertEquals( '+6:30', $offset );
    }

    public function testGetOffsetWithNegativeFraction() {
        $time = new MyTime();
        $offset = $time->get_time_offset_from_number( '-6.5' );
        $this->assertEquals( '-6:30', $offset );
    }

    public function testGetOffsetWithZero() {
        $time = new MyTime();
        $offset = $time->get_time_offset_from_number( '0' );
        $this->assertEquals( null, $offset );
    }

    public function testGetZoneWithZero() {
        $time = new MyTime();
        $zone = $time->get_timezone_from_string( '0' );
        $this->assertEquals( new DateTimeZone( 'Etc/GMT' ), $zone );
    }

    public function testGetOffsetWithPositiveZero() {
        $time = new MyTime();
        $offset = $time->get_time_offset_from_number( '+0' );
        $this->assertEquals( null, $offset );
    }

    public function testGetOffsetWithEmptyString() {
        $time = new MyTime();
        $offset = $time->get_time_offset_from_number( '' );
        $this->assertEquals( null, $offset );
    }

    public function testGetOffsetWithSmallFraction() {
        $time = new MyTime();
        $offset = $time->get_time_offset_from_number( '0.5' );
        $this->assertEquals( '+0:30', $offset );
    }

    public function testGetOffsetWithNegativeSmallFraction() {
        $time = new MyTime();
        $offset = $time->get_time_offset_from_number( '-0.5' );
        $this->assertEquals( '-0:30', $offset );
    }
}