The possessive form of the singular noun railroad is railroad's.
example: The railroad's property ends at the fence.
The B&O Railroad's tracks ran throughout the small town. (one railroad with singular possessive)The railroads' officers were keen to expand rail service in the 1800s. (more than 1 railroad, and plural possessive. This also means that "officers" indicates groups of men, one group per railroad company, but here used as a generic plural, no possessive.)The railroad's conductor got married. (One specific railroad as singular possessive for one specific conductor.)The railroads' conductors were mostly single men. (plural possessive, plural railroad companies with plural conductors).
The singular possessive form of "test" is "test's".
The singular possessive pronouns are mine, yours, his, hers, and its. The singular possessive adjectives are my, your, his, her, and its.
The singular possessive is ant's.The plural possessive is ants'.
Museum is singular. Museum's is singular possessive. Museums is plural. Museums' is plural possessive.
The singular possessive of dish is dish's
Taco's is the singular possessive.
The singular possessive form is classmate's.
The singular possessive is biker's; the plural possessive is bikers'.
The singular possessive is fish's.
Buzz's is the singular possessive.
Grave's is the singular possessive.