Maven Dependency version resolution issue - maven

Question

I'm hitting a problem that confusing me and confounding my understanding of Maven.
I'm using a multi-module project with the structure
root
|_ db/pom.xml
|_ server/pom.xml
The server pom.xml references the db pom.xml. In db/pom.xml I've defined
<dependency>
<groupId>com.zaxxer</groupId>
<artifactId>HikariCP</artifactId>
<version>3.2.0</version>
</dependency>
with the expectation that it'll be inherited by the server. But I'm seeing the server tests complain about a missing method. Sure enough when I use
mvn dependency:tree -Dverbose -Dincludes=com.zaxxer:HikariCP compile
I notice the following.
[INFO] server:war:2.0-SNAPSHOT
[INFO] \- db:jar:2.0-SNAPSHOT:compile
[INFO] \- com.zaxxer:HikariCP:jar:2.5.1:compile (version managed from 3.2.0)
So 2.5.1 is being used for the tests instead of 3.2.0. That explains the complaint about the missing method.
But I'm having trouble identifying where that dependency is coming from? My best guess is that it's coming from starter type of pom.xml that defines it in the test scope.
Any suggestions on how I can identify where this version is defined? I've googled but have not come across a solution.
Working past this issue I decided to also define the following in db
<dependency>
<groupId>com.zaxxer</groupId>
<artifactId>HikariCP</artifactId>
<version>3.2.0</version>
<scope>test</scope>
</dependency>
Meaning I've two definitions of HikariCP in the db pom.xml. Now when I run dependency:tree there are no references to 2.5.1. But... if I try
mvn verify
I get an error in the db
DBConfig.java:[17,25] package com.zaxxer.hikari does not exist
What's going on here?
My expectations are:
The compile scope defined in db should override/win the test scope defined elsewhere (though I can see why that might not be desired)
Defining a compile and test version of HikariCP should not result in a package cannot be found error
---- Updated with requested info ----
db/pom.xml
<modelVersion>4.0.0</modelVersion>
<artifactId>db</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>jar</packaging>
<parent>
<groupId>my.group</groupId>
<artifactId>root</artifactId>
<version>1.0-SNAPSHOT</version>
</parent>
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
</dependency>
<dependency>
<groupId>com.google.guava</groupId>
<artifactId>guava</artifactId>
</dependency>
<dependency>
<groupId>org.postgresql</groupId>
<artifactId>postgresql</artifactId>
<version>42.2.2</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-jdbc</artifactId>
</dependency>
<dependency>
<groupId>javax.inject</groupId>
<artifactId>javax.inject</artifactId>
</dependency>
<dependency>
<groupId>com.zaxxer</groupId>
<artifactId>HikariCP</artifactId>
<version>3.2.0</version>
</dependency>
</dependencies>
server/pom.xml
<modelVersion>4.0.0</modelVersion>
<artifactId>server</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>war</packaging>
<parent>
<groupId>my.group</groupId>
<artifactId>root</artifactId>
<version>1.0-SNAPSHOT</version>
</parent>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-configuration-processor</artifactId>
<optional>true</optional>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-contract-stub-runner</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-tomcat</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>com.jayway.restassured</groupId>
<artifactId>rest-assured</artifactId>
<version>2.9.0</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>my.group</groupId>
<artifactId>db</artifactId>
<version>${project.version}</version>
</dependency>
</dependencies>
The root pom.xml defines no dependencies. But it's parent defines common versions for TPLs, etc that'd be too verbose to list here.
I've also found where hikaricp version 2.5.1 is defined. It's in spring-boot-dependencies. That's likely being introduced by the server's spring-boot-starter-tomcat. But it could also come in through the db's spring-boot-starter-jdbc.
I'll also note that there is no problem if I also define the HikariCP dependency in the server pom.xml.